But yeast-fungi and mould-fungi, like bacteria or fission-fungi, are micro-organisms, belonging to two specific orders, the Saccharomycetes and the Hyphomycetes, which are intimately related to each other, but quite distinct from bacteria. Their germs occur widely distributed in air, soil, and water. Many species are of hygienic, while others are of pathological interest and importance in being either accidentally associated with, or the cause of, disease processes, while others are fermentations of very essential service in various industrial processes. The making of beers, wines, and spirits, as we understand them, constitutes but a small part of the province of fermentation. The life activities of ferments open out a study of vast importance to mankind, and while they have only been regarded in their worst aspect--that of a bane--they are, nevertheless, a boon to mankind. The first clear view we obtained of this was that of Reess, who in 1870 showed there were several species or forms of the yeast-fungus. Hansen followed up this discovery in 1883, and, taking advantage of the strict methods of culture introduced by bacteriologists, found that by cultivating yeast on a solid media from a single spore it was quite possible to obtain constant types of pure yeasts, each possessing its own peculiar properties. One consequence of Hansen’s labours was that it now became possible for every brewer to work with a yeast of uniform type instead of with haphazard mixtures, in which serious disease forms might predominate and injure the beer. Among other things made clear was that a true yeast may have a mycelial stage of development. Furthermore, there is the influence exercised by the nucleus of the yeast cell. Many other points of interest arose out of these investigations; one was, that many higher fungi can assume a yeast-like stage of development if submerged in fluids, as, for instance, various species of Mucor, Ustilago, Exoascus, and numerous others. Ascomycetes, and Basidiomycetes as well, are known to form budding cells, and it was thought that the yeasts of alcoholic fermentation are merely reduced forms of these higher fungi, which have become habituated to the budding condition--a conclusion supported by Hansen’s discovery that a true Saccharomyces can develop a feeble, but a true, mycelium. [Illustration: Fig. 279.--Saccharomyces and Moulds. 1. Section from a tomato, showing spores growing from cuticle; 2. Portion detached to show budding-out process; 3. Lateral view of spore sac with oospores issuing forth; 4. Apiculated ferment spores; 6 and 7. _Mycoderma cerivisiæ_ in different stages of growth, as seen on wine bottles; 8 and 9. _Torulæ diabeticæ_, torulæ and fission spores.]