It has sometimes been supposed that cooked or completely sterilised food (that is to say food that has been subjected to a temperature of from 248°-284° Fahr.) is harmful to the organism and that much of it is not well digested. From this point of view protests have been made against the feeding of infants with sterilised milk or even with boiled milk. Although in certain cases sterilised milk is not well supported by infants, it cannot be doubted but that boiled milk and cooked food are generally successful. The large number of children brought up successfully on boiled cow’s milk and the health of travellers in arctic regions are ample proof of this. I have been told by M. Charcot that in his voyage to the antarctic regions, he and his companions lived entirely on sterilised food, or on cooked food such as the flesh of seals and penguins. As they had no green food nor fresh fruit, the only raw food that they ate was a little cheese. Living under these conditions, all the members of the expedition enjoyed good health, and there was no case of digestive disturbance in the whole period of sixteen months.
It is obvious that abstaining from raw food, and so reducing largely the entrance of new microbes, by no means causes the disappearance of the intestinal flora already existing. We must reckon with that and with the evil that it does by weakening the higher cells of the tissues. As the part of the flora that does most damage consists of microbes which cause putrefaction of the contents of the intestine and harmful fermentations, particularly butyric fermentation, it is against these that our efforts must be directed.
Long before the science of bacteriology was in existence, men had turned their attention to methods of preventing putrefaction. Food, especially if it be kept in a warm place or in a moist atmosphere, soon begins to putrefy and to become unpleasant to the taste and dangerous to the health. Everyone has known cases of poisoning from putrid flesh or other food material. Foà,[128] the explorer of Central Africa, has related that once, when they were starving, he and his men came on the putrefying body of an elephant. The negroes rushed to lay hold of the carrion, but Foà tried to dissuade them, explaining that to eat flesh in such a state was as bad as taking poison. All did not listen to him, and three negroes, who had taken pieces of the body, swallowed them before they had been properly cooked. All three died in a few days, with the neck and throat swollen, the tongue almost paralysed, and the abdomen inflated.
In another case, sausages made of putrid horse flesh caused an epidemic at Rohrsdorf, in Prussia, in 1885.[129] About forty people fell ill after having eaten the sausages, which, according to witnesses, were green in colour, smelt badly, and had a revolting appearance. One person died, whilst the others recovered after cholera-like symptoms. It is true that all putrefying food does not produce the same effect. MM. Tissier and Martelly[130] found no digestive trouble after having eaten food that was quite putrid. Everyone knows that the Chinese prepare a dish particularly pleasant to gourmets by allowing eggs to putrefy. Some decaying cheeses are harmful to the health, but others can be eaten with impunity. The reason of this is that whilst putrefying food may contain microbes and dangerous toxins, it does not contain them in all cases. On the other hand, we must take into account the different susceptibilities of people to the harmful action of microbes and their products. Some can swallow without any evil result a quantity of microbes which in the case of other individuals would produce a fatal attack of cholera. Everything depends upon the resistance offered to the microbes by the invaded organism.
Experiments on animals fed on putrefying food have also given varied results. Some animals eat it without any harm resulting, others have attacks of vomiting and show such a repugnance that it is impossible to continue the experiment.
Not only flesh and other animal substances, but vegetables can undergo putrefaction and fermentation (butyric) which make it dangerous to eat them. Many accidents have occurred in man as the result of deteriorated preserved fruit. Vegetables, preserved in silos to feed cattle, sometimes go wrong. “If, for instance, rainy days come after sunny days, so that the uncovered fodder is wetted again, the resulting ensilage is poor and has an extremely unpleasant butyric odour, so that the animals turn from it.” Sometimes the fodder grows black in the silo, and acquires a special smell. “The animals will take it only in the absence of other food; their excreta become black, and if they are kept on such a diet for a time they waste in a marked manner.”[131]
In popular practice, the value of acids for preserving animal and vegetable food and for preventing putrefaction has long been recognised. Meats of all kinds, fish and vegetables have been “marinated” with vinegar, as the acetic acid in that substance, the product of bacteria, wards off putrefaction. If the materials which it is desired to preserve give off acids themselves, the addition of vinegar may be unnecessary. For this reason some animal products such as milk, or vegetables rich in sugar become acid spontaneously and so can be preserved. Soured milk can be made into many kinds of cheese, and these last for longer or shorter times. Many vegetables can undergo a natural process of souring, when they “keep” without difficulty. Thus cabbage becomes “sauerkraut” and beetroot and cucumbers pass into an acid state. In many countries, as for instance in Russia, the use of acidified vegetables is of great importance in the food-supply of the populace. Fresh fruit and vegetables cannot be obtained in the long winters, during which the people consume large quantities of cucumbers, melons, apples, and other fruits which have undergone an acid fermentation in which lactic acid is the chief product. During summer, milk, which acidifies readily, is the chief source of acid materials for consumption. The chief beverage is “kwass,” of which black bread is the main ingredient, and this passes through not only an alcoholic fermentation, but an acidifying change in which lactic acid is the most important product.
Rye bread, the chief food of the populace, is also a product of fermentations amongst which the lactic acid fermentation is most important, but in other kinds of bread also there is a fermentation in which some of the sugar is transformed to lactic acid.
Soured milk, because of the lactic acid in it, can impede the putrefaction of meat. In certain countries, accordingly, meat is preserved in acid skimmed milk with the result that putrefaction is prevented. Lactic acid fermentation is equally important in the food supply of cattle. It is the chief agent that, in the process of preserving vegetation in silos, hinders putrefaction. Finally, the same fermentation serves in distilleries to preserve the must from which alcohol is prepared.
This short review is in itself enough to show the great importance of lactic fermentation as a means of stopping putrefaction and butyric fermentation, both of which hinder the preservation of organic substances and are capable of exciting disturbances in the organism.