The Microscope. Its History, Construction, and Application 15th ed. / Being a familiar introduction to the use of the instrument, and the study of microscopical science

by Jabez Hogg

Industrial uses of Fungi and Saccharomycetes.

There are many industrial processes which are more or less dependent for success on bacterial fermentations. The subject is young, but the results already obtained are seen to be of immense importance from a scientific point of view, and to open up vistas of practical application already being taken advantage of in commerce, while problems are continually being raised by the forester, the agriculturist, the gardener, the dairyman, the brewer, dyer, tanner, and with regard to various industries, which will eventually confer great advantages in their economic application.

The remarkable discovery made by Alvarez of the bacillus, which converts a sterilised decoction of the indigo plant into indigo sugar and indigo white, the latter then oxidising to form the valuable blue dye, whereas the sterile decoction itself, even in presence of oxygen, forms no indigo, plainly proves how these minute organisms may be turned to a good account. There are, however, important points to be determined as to the action of the fermentation brought about by these enzymes, and the appearance of certain mysterious diseases in the indigo vats. Again, certain stages in the preparation of tea and tobacco leaves are found to depend upon very carefully regulated fermentations, which must be stopped at the right moment, or the product will be spoilt. Regarding the possible rôle of bacteria, the West Indian tobacco has a special bacterium, which has been isolated and found to play a very important part in its flavour. Every botanist knows that flax and hemp are the best fibres of Linum and Cannabis respectively, separated by steeping in water until the middle lamella is destroyed and the fibres isolated; but it is not so well known that not every water is suitable for this “retting” or steeping process; and for a long time this was as much a mystery as why some waters are so much better than others for brewing. Quite recently Fribes has succeeded in isolating the bacillus upon which the dissolution of the middle lamella depends. This investigation brought out other interesting details as to the reaction produced by living micro-organisms, and which can be utilised in deciding questions of plant chemistry too subtile for testing with ordinary re-agents. One other important fact connected with these researches is that botanists have now discarded the view that the middle lamella of the plants referred to is composed of cellulose, and know that it consists of pectin compounds. Fribes’ anærobic bacillus is found to dissolve and destroy pectins and pectinates, but does not touch cellulose or gum. It is well known that the steeping of skins in water in preparation for tanning involves bacterial action, owing to which the hair and epidermal coverings are removed, but it also appears that in the process of swelling the limed skins, the gases evolved in the substance of the tissues, and the evolution of which causes the swelling and loosens the fibre so that the tanning solutions may penetrate, are due to a particular fermentation caused by a bacterium, which, according to some investigators, is identical with a lactic ferment introduced by the pine bark, and which is responsible for the advantageous acidification of the tanning solutions.

Hay is made in different ways, and in those where a “spontaneous” heating process is resorted to the fermentation is no doubt dependent upon the presence of thermogenic bacteria. But probably no other subject has attained to so much importance as the bacteriology of the dairy: the study of the bacteria found in milk, butter, and cheese in their various forms.

Of milk, especially, much has been written and said as a disease-transmitting medium, and with every good reason, and, if the statement of a Continental authority may be accepted that each time we eat a slice of bread and butter we devour a number of bacteria equal to the population of Europe, we have sure grounds for seeking for further information as to what these bacteria are and what they are doing. And similarly so with cheese, which teems with millions of these minute organisms.

“Some few years ago it was found that the peculiar aroma of butter was due to a bacterium. There are two species of bacteria, one of which develops an exquisite flavour and aroma, but the butter keeps badly, while the other develops less aroma, but the butter keeps better. In America, however, they have isolated and distributed pure cultures of a particular butter bacillus which develops the famous ‘June’ flavour, hitherto only met with in the butter made in a certain district during a short season of the year. This fine-flavoured butter is now constantly manufactured in a hundred American dairies; and the manufacture of pure butter with a constant flavour has become a matter of certainty.

“Properly considered, the manufacture of cheese is a form of ‘microscopic gardening’ even more complex and more horticultural in nature than the brewing of beer. From the first moment, when the cheesemaker guards and cools his milk, till his stock is ready he is doing his best to keep down the growth of micro-organisms rushing about to take possession of his milk. He therefore coagulates it with rennet—an enzyme of animals, but also, as we have seen, common in plants—and the curd thus prepared is simply treated as a medium, on which he grows certain fungi and bacteria, with every needed precaution for favouring their development, and protecting them against the inroads of other pests and against unsuitable temperature, moisture, and access of light. Having succeeded in growing the right kind of plants on his curd, his art then demands that he shall stop their growth at the critical moment, and his cheese is ready for market.

“Furthermore, the particular flavour and peculiar odours of cheeses, as Camembert, Stilton, and Roquefort, have to be obtained, and this is secured, for instance, by cultivating a certain fungus, Penicillium, on bread, and purposely adding it to Roquefort. This is found to destroy the lactic and other acids, and so enables certain bacteria in the cheese to set to work and further change the medium; whereas in another kind of cheese the object is to prevent this fungus paving the way for these bacteria. Another kind of bacillus has been discovered which gives a peculiar clover aroma to certain cheeses.

“It is thought that more definite results will be obtained by the investigation of the manufacture of the vegetable cheeses of China and Japan, which are made by exposing the beans of the leguminous plant, Glycine—termed soja-beans—to bacterial fermentations in warm cellars with or without certain mould-fungi. Several kinds of bean-cheeses are made in this way, known by special names. They all depend upon the peculiar decompositions of the tissues of the cotyledons of the soja-beans, which contain 35 to 40 per cent. of proteids and quantities of fatty matter. The softened beans are first rendered mouldy, and the interpenetrating hyphæ render the contents accessible to certain bacteria, which peptonise and otherwise alter them. There is the further question of the manufacture of vinegar by fermentation, of the preparation of soy from a brine extract of mouldy and fermented soja-beans, of bread-making, and other equally interesting manufactures.”