CHAPTER II
FERMENTED MILKS
There is considerable variety in the number of soured or fermented milks, and they are known by various names, such as Koumiss or Koomiss, which is prepared from mares' milk; Keffir, which was originally discovered in the mountains of the Caucasus, and which is prepared with Keffir grains; Leben, an Egyptian product prepared from the milk of the buffalo, cow, or goat; Matzoon, a soured milk which is prepared in Armenia from ordinary cows' milk; Dadhi, an Indian preparation from cows' milk. All of these owe their special characteristics to the fact of their having undergone lactic and alcoholic fermentation.
"Milk left to itself," says Blyth,[14] "at all temperatures above 90° F. begins to evolve carbon dioxide, and this is simply a sign and result of fermentation. If this fermentation is arrested or prevented, the fluid remains perfectly sweet and good for an indefinite time. Besides the production of carbon dioxide during decomposition, a certain portion of milk sugar is converted into lactic acid, some of the casein and albumen are broken up into simpler constituents, and a small proportion of alcohol produced, which by oxidation appears as acetic acid, while the fat is in part separated into free fatty acids, which ultimately unite with the ammonia produced by the breaking up of the albuminoids. The main fermentation of milk is a special kind which of late years has been much studied, and is known as lactic fermentation. Accompanying lactic fermentation there is nearly always a weak butyric and a weak alcoholic fermentation."
One of the organisms causing Butyric Acid Fermentation is a bacillus 3 to 10µ in length, and about 1µ in breadth. It has power of movement, and when cultivated in gelatine, liquefies the gelatine, forming a scum on the surface. When the bacillus is sown into sterile milk, the following, according to Hueppe, are the changes:
"If the milk thus infected is incubated, on the second day a clear, slightly yellow fluid is seen under the layer of cream; this fluid increases from day to day, so that gradually a column of fluid is formed which is quite clear above, but below is turbid; the casein, at first thrown down in a firm coagulum, in the course of eight days begins to be attacked, and by the end of two or three weeks most of it is dissolved. The filtered fluid gives the biuret reaction; it contains leucin, tyrosin, and ammonia; hence it is clear that the ferment acts to some extent as a digestive of albumen. In advanced butyric acid fermentation, the fluid is most offensive, and may have an alkaline reaction."
Lactic acid was first isolated by Scheele in 1780 from soured milk, but its exact constitution was not determined until later by Liebig, Mitscherlich, Gay-Lussac, and Pelouze: "It is widely distributed in nature, occurring in the sap of the vine and in most fermented liquids, especially in soured milk; it is not, however, present in fresh milk."[15]
In all the Eastern preparations referred to, the lactic fermentation is produced, followed by alcoholic fermentation, which is due to the slow decomposition of the milk sugar, the vinous fermentation being most readily set up in milks which contain a larger relative proportion of milk sugar and water, such as the milk derived from the mare, the sheep, and the camel. As these fermented milks have different characteristics, it is necessary to the thorough understanding of the process of manufacture at the present day, to examine them in some detail.
Koumiss.—The greatest of all the fermented milks is koumiss, and it has been celebrated from the most ancient times until the present day, as being the principal food of the wandering tribes of Khirgiz, Bashkirs, Kalmucks, and Tartars, who inhabit the steppes of European Russia and the plains of South, Western, and Central Asia. According to Carrick, who has written an interesting volume on the subject,[16] the nomads who inhabit these vast territories are shut up under the most miserable circumstances during the winter time and at the advent of spring they roam over the steppes from morning to night, usually in the saddle. The milk yielded at such time by the mares is carefully collected, and these nomads consume enormous quantities of it in the fermented state, this habit having been in existence amongst them from time immemorial. It is said that the Scythians, long before the Christian era, used fermented mares' milk; and there are ornaments in existence in Russia, of Scythian origin, which exhibit in detail the preparation of koumiss from mares' milk. In historical times, the first mention of koumiss was in the twelfth century, when it is referred to in the Ipatof Chronicles. During the thirteenth century William de Rubruquis, a French missionary, wrote about his travels in Tartary, and he described how he had first become acquainted with koumiss, and how he found it savoury to the palate. Subsequent to this, however, there is very little mention of koumiss in Russian history, or, for that matter, in any other, and the first really scientific contribution on the subject was by Dr. John Grieve, who was a surgeon in the Russian army, and who in the year 1784 sent a description of koumiss to the Royal Society of Edinburgh,[17] of which he was a member, and the title of it was, "An Account of the Method of Making Wine called by the Tartars Koumiss, with Observations on its Use as a Medicine." Dr. Grieve strongly advocated the use of koumiss as beneficial in cases of wasting diseases, and subsequently it was adopted by the medical profession, with the result that sanatoria for the treatment of pulmonary consumption were established at Samara and other places in Russia, and met with very great success; and at the present day such sanatoria are carried on, but the bacteriology of the subject now being thoroughly understood, the methods of preparation have been somewhat modified.
An interesting account of koumiss is given by Clarke,[18] who says:
"Everybody has heard of koumiss, and the brandy which the Kalmucks are said to distil from the milk of mares. The manner of preparing these liquids has been differently related, and perhaps is not always the same. They assured us that the brandy was merely distilled from buttermilk. The milk which they collect overnight is churned in the morning into butter; and the buttermilk is distilled over a fire made with the dung of their cattle, particularly the dromedary, which makes a steady and clear fire like peat. But other accounts have been given both of the koumiss and the brandy. It has been usual to confound them, and to consider the koumiss as their appellation for the brandy so obtained. By other information I could gain, not only here, but in many other camps which we afterwards visited, they are different modifications of the same thing although different liquors; the koumiss being a kind of sour milk, like that so much used by the Laplanders called pina, and which has undergone, in a certain degree, the vinous fermentation; and the brandy an ardent spirit obtained from koumiss by distillation. In making koumiss they sometimes employ the milk of cows, but never if mares' milk can be had, as the koumiss from the latter yields three times as much brandy as that made from cows' milk.
"The manner of preparing the koumiss is, by combining one sixth part of warm water with any given quantity of warm mares' milk. To these they add, as a leaven, a little old koumiss, and agitate the mass till fermentation ensues. To produce the vinous fermentation, artificial heat and more agitation is sometimes necessary. This affords what is called koumiss. The subsequent process of distillation afterwards obtains an ardent spirit from the koumiss. They call it vina. In their own language it bears the very remarkable appellation of rack and racky, doubtless nearly allied to the names of our East India spirit rack and arrack. We brought away a quart bottle of it, and considered it very weak bad brandy, not unlike the common spirit distilled by the Swedes and other northern nations. Some of their women were busy making it in an adjoining tent. The simplicity of the operation and their machinery was very characteristic of the antiquity of this chemical process. Their still was constructed of mud, or very coarse clay; and for the neck of the retort they employed a cane. The receiver of the still was entirely covered by a coating of wet clay. The brandy had already passed over. The woman who had the management of the distillery, wishing to give us a taste of the spirit, thrust a stick, with a small tuft of camel's hair at its end, through the external covering of clay, and thus collecting a small quantity of the brandy, she drew out the stick, dropped a portion on the retort, and, waving the instrument above her head, scattered the remaining liquor in the air. I asked the meaning of this ceremony, and was answered that it is a religious custom to give always the first drop of the brandy which they draw from the receiver to their God. The stick having been plunged into the receiver again, she squeezed it into the palm of her dirty and greasy hand, and after tasting the liquor, presented it to our lips."
Another interesting account of the preparation of koumiss is given by John M. Wilson in the Rural Encyclopædia,[19] and it shows that the methods in use about the middle of last century did not differ materially from those which existed centuries before.
Wilson says: "Khoumese is vinously fermented mares' milk. Any quantity of fresh mares' milk is put into wooden vessels; a sixth part of water just off the boil is mixed with it; an eighth part of old khoumese or of the sourest possible cows' milk is added; the mixture is kept from fifteen to twenty-four hours, covered up with several folds of coarse linen cloth and with a very thick board, and without being stirred or in any degree disturbed, in a moderately warm place till it becomes thoroughly sour, and sends up a thick mass to its surface; it is then beaten and pounded and stirred till the curd is not only broken, but so thoroughly mixed with the serum as to form a thick liquid; it next remains covered and at rest during twenty-four hours more, and it is finally put into a common butter churn and beaten and blended into a state of perfect homogeneity. It is now fit for use; yet it acquires an increase of given properties if it be allowed to stand for a few days, and either then or now it would, if distilled, yield nearly one third of its own bulk of a weak spirit which will bear to be rectified. Whenever it is used it must be previously so agitated that its component parts may be well mixed together, and it may be kept either in pans for immediate use or in casks for more remote use; and if placed in a cool cellar it will remain good during three or four months."
Mares' milk owes its peculiar fitness for making koumiss to its containing a large proportion of sugar of milk, and readily undergoing the vinous fermentation, and it possesses a general medicinal reputation among the Tartars similar to that which asses' milk has partially acquired in Britain. "That mares' milk will undergo vinous fermentation and yield a certain quantity of spirit," says a writer in the Magazine of Domestic Economy, "is not generally known, and it was reserved for a nation of demi-savages to render this circumstance available as an agent of health, as well as an agreeable and nourishing beverage. Every educated person, however, has heard that the Tartars drink mares' milk, though few know that this milk is taken on account of its specific virtues alone, and not as a substitute for cows' milk, of which they have abundance, and with which they adulterate mares' milk when scarce." But the koumiss is reputed to be much more medicinal than the mares' milk itself; and on account of its being free from all tendency to curdle in the stomach, and of its possessing most of the nutritive power of the milk in combination with native fermented spirit, it has been strongly recommended by some persons as a remedy for most or all cases of general debility, of nervous languor, and even pulmonary disease.
"Khoumese is called sometimes koumiss and sometimes milk wine."
From these references it will be seen that koumiss is an alcoholic drink made by the fermentation of mares' milk, but it is also frequently prepared from the milk of the camel and cows' milk. It is stated that a similar preparation to Russian koumiss is made in Switzerland from cows' milk simply by the addition of a little sugar and yeast to skim milk; "it contains more sugar and less lactic acid than Russian koumiss, and on account of the much greater proportion of casein contained in cows' milk, differs considerably from that prepared from mares' milk." Suter-Naef gives the composition of a Swiss koumiss[20] manufactured at Davos as follows:
| In Grams. | Per Litre. | ||
| Per cent. | (by weight.) | ||
| Water | 90.346 | 1019.64 | grams. |
| Alcohol | 3.210 | 36.23 | " |
| Lactic acid | 0.190 | 2.14 | " |
| Sugar | 2.105 | 23.75 | " |
| Albuminates | 1.860 | 20.99 | " |
| Butter | 1.780 | 20.09 | " |
| Inorganic salts | 0.509 | 5.74 | " |
| Free carbonic acid | 0.177 | 2.00 | " |
The ferments used in the preparation of koumiss are stated by Carrick to be of two different kinds, artificial and natural.
"Of the natural ferments two have been resorted to. One is mentioned by Grieve, which he borrowed from the Bashkirs of Orenbourg, and which simply consists in the addition of one sixth part of water and one eighth of the sourest cows' milk to fresh mares' milk; the other has been employed, and was, if I mistake not, first recommended by Bogoyavlensky. It is a very simple if rather a tedious method. New mares' milk, diluted with one third its bulk of water, is placed in the saba,[21] and while allowed to sour spontaneously, is continually beaten up. This milk gradually undergoes the vinous fermentation, and in twenty-four hours is converted into weak koumiss. The disadvantage of this mode of commencing fermentation is obvious—viz., the great waste of time in agitation. Hence it is only employed when no artificial ferment is obtainable.
"In starting the process of fermentation in mares' or any other kind of milk, therefore, an artificial ferment is more frequently employed than a natural one. The former is used only for converting the first portion of milk into koumiss; the latter is always resorted to afterwards.
"Of artificial ferments the variety is great, for besides all putrefying animal matters which contain nitrogen—such as blood, white of egg, glue, and flesh—certain mineral substances which act by souring the milk are also capable of exciting fermentation.
"Now, many of the nomads, whose mares either give no milk or are not milked in winter, commence the preparation of their koumiss in spring by borrowing a ferment from the animal, mineral, or vegetable kingdom. Thus a mixture of honey and flour is the favourite ferment with some races of nomads; a piece of fresh horse-skin or tendon is preferred by others, while a few resort to old copper coins, covered with verdigris, for starting fermentation. In the choice of a ferment they are guided solely by habit and tradition. As it would be useless, almost impossible, to give a list of all the foreign substances that have been employed with the view of converting mares' milk into koumiss, it will be best to consider the simplest artificial ferments, and those most generally in use.
"The simplest way is that recommended by Bogoyavlensky, and adopted and modified by Tchembulatof.[22] It is prepared thus: 'Take a quarter of a pound of millet-flour, add water to it, and boil it down to the consistence of thick oatmeal porridge. Then heat separately, in another vessel, eleven pints of milk to boiling-point, and allow it to cool down. When its temperature has fallen to 95° F., pour it into a wooden bowl or tub, and add the boiled flour to it. The upper and open part of the vessel is then covered with a piece of coarse linen, and left at rest—at a temperature of about 99° F.—from twenty-four to forty-eight hours. The appearance of small bubbles, which keep bursting on the surface of this liquid, combined with a vinous or acid odour, prove that the ferment is ready. To this fermenting fluid twenty-two quarts of new milk are gradually (i.e., every ten minutes) added, and the whole mass is continuously beaten up for twelve hours. The temperature during stirring should never be higher than 94° F. The whole fluid soon begins to ferment, and after twelve hours a not unpleasant koumiss is ready. This should be filtered through a horse-hair or muslin sieve, after which it is fit for drinking. This liquid is called weak koumiss; but a limited portion of the lactine has undergone the lactuous and vinous fermentations, and thus the percentage of alcohol is small. Koumiss at an ordinary temperature remains weak for twelve hours after it has been beaten up, and then gradually passes into medium.'"
Curiously enough, the richness of cows' milk in fat militates against its being a good raw material for the making of koumiss, owing to the production of small quantities of butyric acid, which follows upon the fermentation, so that it is desirable, if koumiss is to be prepared from cows' milk, that the fat should be first of all eliminated, so that the separated milk will then approximate to the composition of mares' milk.
"The chemical changes," says Hutchison,[23] "which take place in the milk under the double fermentation are not difficult to follow; the lactic ferment simply changes part of the sugar into lactic acid, the vinous ferment eats up a very small part of the proteid of the milk, and, at the same time, produces from the sugar a little alcohol and a good deal of carbon dioxide; the milk thus becomes sour, it effervesces and is weakly alcoholic, but the lactic acid causes the casein to be precipitated just as it does in the ordinary souring of milk, and the casein falls down in flocculi."
As will have been noticed, it is an essential part of the process of koumiss-making to keep the milk in a state of agitation during the period of fermentation, a process which is intended to permit of oxygen being taken up by the fermenting fluid, while, at the same time, the casein is broken up into a state of fine division. The casein also, or at least a portion of it, becomes very soluble, and after twelve hours of fermentation the taste of the product is only slightly sour, and the milk taste still remains. This taste, however, disappears in twenty-four hours, owing to the rapid development of the lactic acid organisms. After this lapse of time the sugar is entirely destroyed, and the strong koumiss which results is a thin sour fluid which effervesces briskly, and in this condition will keep for an indefinite period. "The net change which has taken place in the original milk may be summed up by saying that the sugar of the milk has been replaced by lactic acid, alcohol, and carbon dioxide, the casein has been partly precipitated in a state of very fine division, and partly pre-digested and dissolved, while the fat and salts have been left much as they were."[24]
Violent stirring or agitation of the cultures does not seem to work so much by supplying oxygen to the fermenting liquid, as by ensuring a thorough distribution of the micro-organisms throughout the liquid, and thus dividing the casein.
The greater number of the organisms are facultative anærobes and oxygen is not necessary. Again, koumiss put up in bottles on the first day is regularly shaken although air is excluded.
Keffir.—Keffir is a kind of fermented milk which has been in use in the Caucasus for quite a long time, as koumiss has been in the steppes. It differs from koumiss, however, in this respect, that it is prepared from either sheep's, goats', or cows' milk. The process is started by the addition of keffir grains to the milk, which is contained in leathern bottles. These keffir grains are small solid kernels which are kept in families and handed on from one generation to another.[25] The grains are the origin of the ferment, as they disseminate in the milk micro-organisms of a lactic yeast (Saccharomyces kefir Beyerinck and Freudenreich) and also the bacillus Bacterium caucasicum, which develop rapidly and split up the milk sugar into carbon dioxide, alcohol, and lactic acid. Small quantities of glycerine, acetic, succinic, and butyric acids are also formed, the casein and albumen being partly peptonised.[26] Keffir becomes slightly effervescent in twenty-four hours, and in that time develops a small quantity of alcohol, but after three days the amount of alcohol and lactic acid is much increased.[27] It has been determined that the fermentation of the milk is due to Saccharomyces kefir, and that the Lactobacillus Caucasicus does not take any part in the fermentation, a fact which seems to be supported by the capacity of ordinary keffir for starting the fermentation in fresh milk in the same manner as the keffir grains. The use of this beverage seems to be universal throughout the Caucasus, and travellers in these regions have frequently referred to it. Thus Freshfield[28] states in one part of his book of travels as follows:
"The pig-faced peasant against whom we had at first sight conceived such an unjust prejudice turned out a capital fellow. He brought us not only fresh milk, but a peculiar species of liquor, something between public-house beer and sour cider, for which we expressed the greatest admiration, taking care at the same time privately to empty out the vessel containing it, on the first opportunity." And again:
"The hospitable shepherds regaled us, not only with the inevitable and universal airam or sour milk—if a man cannot reconcile himself to sour milk, he is not fit for the Caucasus—but with a local delicacy that has lately been brought to the knowledge of Europe—kefir. This may best be described as 'effervescing milk.' It is obtained by putting into the liquid some yellow grains, parts of a mushroom which contains a bacillus known to science as Dispora caucasia. The action of the grains is to decompose the sugar in the milk, and to produce carbonic acid and alcohol. The grains multiply indefinitely in the milk; when dried they can be preserved and kept for future use; its results on the digestion are frequently unsatisfactory, as one of my companions learnt to his cost."
"It has been supposed," says Metchnikoff, "that the chief merit of kephir was that it was more easy to digest than milk, as some of its casein is dissolved in the process of fermentation. Kephir, in fact, was supposed to be partly digested milk. This view has not been confirmed. Professor Hayem thinks that the good effects of kephir are due to the presence of alcoholic acid, which replaces the acid of the stomach and has an antiseptic effect. The experiments of M. Rovigh, which I speak of in The Nature of Man, have confirmed the latter fact, which now may be taken as certain. The action of kephir in preventing intestinal putrefaction depends on the lactic acid bacillus which it contains. Kephir, although in some cases certainly beneficial, cannot be recommended for the prolonged use necessary, if intestinal putrefaction is to be overcome.... Professor Hayem prohibits its use in the case of persons in whom food is retained for long in the stomach. When it is retained in the stomach, kephir goes on fermenting, and there are developed in the contents butyric and acetic acids, which aggravate the digestive disturbances. Kephir is produced by combined lactic and alcoholic fermentations ... and it is the lactic and not the alcoholic fermentation on which the valuable properties of kephir depend; it is correct to replace it by sour milk, that contains either no alcohol or merely the smallest traces of it. The fact that so many races make sour milk and use it copiously is an excellent testimony of its usefulness."
There are two methods given by Flügge[29] for the preparation of keffir:
"In the first, the dry brown kefir grains of commerce are allowed to lie in water for five or six hours until they swell; they are then carefully washed and placed in fresh milk, which should be changed once or twice a day until the grains become pure white in colour and when placed in fresh milk, quickly mount to the surface—twenty to thirty minutes. One litre of milk is then poured into a flask, and a full tablespoonful of the prepared körner added to it. This is allowed to stand open for five to eight hours; the flask is then closed and kept at 18° C. It should be shaken every two hours. At the end of twenty-four hours the milk is poured through a fine sieve into another flask, which must not be more than four fifths full. This is corked and allowed to stand, being shaken from time to time. At the end of twenty-four hours a drink is obtained which contains but little carbon-dioxide or alcohol. Usually it is not drunk until the second day, when, upon standing, two layers are formed, the lower milky, translucent; and the upper containing fine flakes of casein. When shaken it has a cream-like consistence. On the third day it again becomes thin and very acid. The second method is used when one has a good kefir and two or three days to start with. Three or four parts of fresh cows' milk are added to one part of this and poured into flasks which are allowed to stand for forty-eight hours with occasional shaking. When the drink is ready for use, a portion (one fifth to one third) is left in the flask as ferment for a fresh quantity of milk. The temperature should be maintained at about 18° C., but at the commencement a higher temperature is desirable. The grains should be carefully cleaned from time to time and broken up to the size of peas. The clean grains may be dried upon blotting-paper, in the sun, or in the vicinity of a stove; when dried in the air they retain their power to germinate for a long time."
Leben.—In our earlier references to fermented milks in scriptural times, we observed that alcoholic fermented milks were not permitted to be presented at the altar. Such offerings, however, were quite allowable amongst the ancient Egyptians, the Arabs and Carthaginians,[30] and from remote antiquity these nations placed great value on this product. Leben, which is peculiarly associated with Egypt, is a soured milk prepared from the milk of buffaloes, cows, or goats. It is usually prepared by the boiling of the fresh milk over a slow fire, after which some fermented milk from a previous preparation is added to the warm article, and the fermentation takes place rapidly and is considered to be complete in about six hours.[31] The Egyptian leben is valued so highly that it is offered in hospitality to the passing stranger, and it is regarded as so much of a duty to present this milk, that in some parts of Arabia it would be looked upon as scandalous if any payment were received in return.[32]
Matzoon.—Matzoon is prepared in Armenia in somewhat the same manner as keffir is prepared in the Caucasus, and indeed it differs very slightly from keffir in composition. Its use is universal in Armenia.
Dadhi.—In India large quantities of fermented milk are used, under the name of Dadhi, and its characteristics are not unlike the similar products in Europe. The specific bacillus has been investigated by Chatterjee,[33] who concludes that it is somewhat akin to the Bacillus bulgaricus and the bacillus of leben (B. lebenis). Dr. Chatterjee gives a résumé of his investigations which sums up the whole matter thus:
"1. The fermented milk of India called Dadhi resembles in all essential points the Bulgarian fermented milk as well as the leben and other forms of fermented milk in use in the East.
"2. The causative element of the curdling process of Dadhi is a streptothrix having characters similar to the Bacillus bulgaricus and Streptobacilli lebeni, and Bacillus caucasina and the Long Bacilli of Mazun, in (1) not growing in ordinary media; (2) producing a large amount of lactic acid in milk; (3) producing, besides coagulation of casein and splitting up the sugar of milk into lactic acid, no other change in milk; (4) not producing any indol, nor peptone, nor saponification of fat, nor formation of any gas.
"3. It differs from the above by showing peculiar pink-stained granules, when stained with methylene blue and showing peculiarly convoluted chains in glucose agar.
"4. The importance of the organism lies in the fact that, as in the case of Bacillus bulgaricus, it kills all pathogenic non-sporing germs and also destroys all proteolytic gas-forming bacilli in milk."
In the account of these investigations the following table is given, showing the amount of lactic acid produced by different lactic acid bacilli in one litre of milk, in terms of lactic acid—the culture being kept at 37° C.
| Name of the Bacillus | After 24 Hours | After 48 Hours | After 72 Hours | After 96 Hours | After a Week | Remarks |
| B. lactis ærogenes | 1.8 | ... | 10.08 | ... | ... | Observed by Hall and Smith |
| B. coli communis | 1.8 | ... | 4.77 | ... | ... | Observed by Hall and Smith |
| B. Bulgaricus | 12.8 -.4 | 16.5 -.4 | 20.2 -.4 | ... ... | 22.0 -.4 | Observed by Gabriel Bertrand and Weisweller; the initial acidity of the milk was 4. |
| Matzoon Long stäbschen B. | 10.8 | 12.0 | ... | ... | ... | Observed by Düggeli |
| Streptobacillus lebenis | 2.61[34] | ... | ... | ... | ... | Observed by Rist and Khoury |
| Streptothrix dadhi | 10.8 | 1.08 | 11.25 | 11.70 | 18.5 | Medd. Coll. Calcutta |
In different parts of the world sour milk is consumed in great quantities, and it is stated by Metchnikoff[35] that the chief food of the natives of tropical Africa consists of soured milk, and in Western Africa in the region south of Angola, the natives live almost entirely on this product, there being a difference in the curdled milks produced according to the nature of the microbial flora which is introduced.
It is stated[36] that in Servia, Bulgaria,[37] and Roumania there were 5000 centenarians living in 1896, and while many reasons are advanced for such an abnormal condition of affairs, it seems fairly certain that the sole reason why people in these districts live to such great ages is because of their mode of living and the fact that they live very largely on soured milk. The hygienic conditions throughout these countries are not such as would give the population in the towns and villages any special advantages in the prolongation of life, and while it may be stated that a pastoral and agricultural life are likely to contribute to longevity, these conditions would not account for a general tendency to live long in the countries referred to, more than in any other agricultural area. There are many countries throughout the world in which the pastoral and agricultural existence is general, but it has not been shown that in these countries life is prolonged. Hence the conclusion has been forced upon investigators that the reason is to be found not in the pastoral conditions, but in the habit which has existed from time immemorial of consuming sour milk as a principal article of diet.
There is no curtailment of the use of fermented milks in Eastern Europe, and the methods of preparation at the present day are those which have been carried out from time immemorial. A local observer states that in Bulgaria yoghourt is made in nearly every household, especially in the spring and summer. The method of preparation is very simple: The milk is boiled until a quarter of its volume has evaporated, it is then cooled to 45° C. and the ferment added. This ferment is a portion of the yoghourt of good flavour and is called "Maya" or "Zakvaska." The vases, a kind of earthenware pot, are enveloped in woollen stuff or sheepskin and placed in a warm place near the chimney. In ten hours the yoghourt is made, and it is preserved in a cold place. The great reputation that the yoghourt has acquired in Western Europe has caused this "Maya" to become an article of commerce. It is sent out by rail hermetically sealed in tinplate boxes. According to a Sophia chemist, the "Maya" is employed in the following manner: For a litre of milk it is necessary to take about 10 gr. of the ferment. This ferment is diluted with three times the amount of water and put into a bowl previously heated with hot water and dried. Into this bowl the milk, previously boiled and cooled to a temperature of 75° to 50° C., is poured; it is then covered over and put in a temperature of about 30° C., and, in default of a stove of constant temperature, the bowl is wrapped round with flannel or a plaid, and left to curdle for eight to ten hours. It is then ready for consumption. During winter, curdled milk keeps for several days, and in summer it becomes sour in from twelve to twenty-four hours.
A similar food to the yoghourt is prepared in the Balkan mountains from sheep's milk under the name of "Urgoutnik."[38] The milk is poured into a goatskin or sheepskin bag, and a little of the fermented milk added, and is then left for some hours in a warm place. The milk consumed is replaced by a fresh supply. In some of the Balkan countries, they are not content with the fermentation of the milk, they add a little alum, which, under the name of "typsa," is well known for this purpose. The milk attains such a solid consistency that it can be put into a cloth and carried to market.[39]
The various forms of sour milk which have been described in the foregoing pages may be said to be of the traditional kind, and with the light of modern knowledge, it has been possible to determine exactly what constitutes the active principle in use in the milk consumed in these countries, and, as we shall see, this principle has been applied so that, at the present day, a pure fermented milk may be obtained in any country, and there is every reason to believe that should such be adopted as a general article of food, it would contribute to the prolongation of human existence.
It is due to Metchnikoff, of the Pasteur Institute, that so much prominence has been given to the use of fermented milks. He gave it as his opinion[40] that senility was caused partly by auto-intoxication or by the poison derived from putrefactive micro-organisms which inhabit the digestive track. These organisms increase with age, and under certain unhealthy conditions multiply enormously, particularly in the large intestine. Having arrived at this knowledge, Metchnikoff set to work to devise some means of combating the influence of these harmful microbes, and set up the hypothesis that the tendency to longevity which is exhibited in Eastern countries is due to the consumption of lactic acid organisms in the shape of soured milk. These organisms are more powerful than those of a putrefactive character and inhibit their growth.
"In the presence of such facts," says Metchnikoff, "it becomes exceedingly important to find some means of combating the intestinal putrefaction which constitutes so incontestable a source of danger. Such putrefaction is not only capable of producing diseases of the digestive tube—enteritis and colitis—but even of becoming a source of intoxication of the organism in its most varied manifestations.
"It is some years since I proposed to combat intestinal putrefaction and its injurious consequences by means of lactic ferments. I thought the acidity produced by such microbes would be much more effective in preventing the germination of putrefying microbes than the small quantity of acids produced by Bacillus coli. On the other hand, I had no illusion as to the difficulty sure to be encountered in any effort to introduce lactic microbes into the intestinal flora which has been preoccupied by a multitude of other microbes. To make surer of the result, I chose the lactic microbe, which is the strongest as an acid producer. It is found in the yahourt (yoghourt), which originates in Bulgaria. The same bacillus has also been isolated from the leben of Egypt; and it is now proved that it is found in the curdled milk of the whole Balkan peninsula, and even in the Don region of Russia."[41]
It is a short step from considerations like these to the adoption of the Bacillus bulgaricus as the most potent of the various lactic organisms which have been examined, and which is likely to play such an important rôle in the destiny of the human race. The Bacillus bulgaricus may claim to be the Bacillus of Long Life.