The chemical process of nutrition in funguses is not the same as in other vegetables. Funguses do not convert inorganic matter into organic compounds, They possess a vital force capable of overcoming the natural play of chemical affinities, and they live by appropriating the constituents of the compounds they are thus enabled to decompose, Fermentation is nothing more than the manifestation of this process of decomposition. Such fermentations as are not produced by the immediate action of living cells are called indirect. They are caused by the intervention of nitrogenous soluble matters elaborated by living cells. These soluble ferments are often stored up till circumstances require their alternative action. It would seem that most organic substances are subject to fermentative changes, often occasioned by a special ferment plant. There are other ferment plants besides those that are recognised as funguses. Sugar undergoes several direct fermentations—the alcoholic, lactic, vinous, and butyric. Alcohol by fermentation becomes acetic acid; albuminous matters and urea are transformed into ammonia by processes of fermentation.
It will be interesting to sanitarians to know that there is reason for believing that the conversion of ammonia into nitric acid is caused by the presence of a fungus: this process has been called nitrification. It goes on constantly in soil that is saturated with decomposing animal matter. The saltpetre of commerce is for the most part imported from India, and is obtained by washing it out of the soil. Nitrification has long been known and carried on artificially. Pasteur suggested that it might be a fermentative change, and soma recent experiments show that be was probably correct. MM. Muntz and Schliessing passed sewage water through a porous medium; for eight days there was no change in the amount of ammonia, but after that time ammonia disappeared and nitric acid took its place. This experiment is only explicable by supposing that germs of a ferment plant were present and took time to mature. This notion was confirmed by another experiment, which proved that the presence of antiseptic vapours suspended the action.
Among fermentations the alcoholic takes the first rank; it is the most familiar and the most easily studied. There has been considerable differences of opinion as to the nature of the plant which causes this fermentation, Most English authorities have considered till lately that it was a modified growth of a common mould called Penicillium. German mycologists make it into a genus belonging to the class Torulæ among funguses. They call the genus Saccharomyces, and include within it several species.
Common yeast is Saccharomyces cerevisiæ; the composition bakers use has very small cells and is called S. minor. The yeast that grows on malt liquor when left to spontaneous fermentation, as is the practice in Belgium, is S. apiculatus. Other species appear on musts of wines, and juices of stone fruit. The species that is so important in this district, because it affects the transformation of apple juice into cider, appears under the microscope to be identical with that which is found on malt liquor, viz., S. apiculatus. Pasteur has proved by a simple experiment that germs or spores of Saccharomyces exist on the surface of grapes. He
