SACCHAROMYCETES 623 
within the intact maternal cell. At sponilation each ascospore 
develops into a mature yeast cell, consequently sporulation in this 
group is, in a sense, a process of reproduction, for each ascospore is 
potentially equivalent to a bud in that it develops into a complete 
vegetative cell. 
The yeasts are of considerable importance commercially; some 
varieties are extensively used in the fermentation of malt and others 
are employed in the manufacture of bread. In either case the organism 
liberates carbon dioxide from carbohydrates, and alcohol as well. 
This activity is brought about by an intracellular enzyme, "zymase," 
which may be obtained in an active state, free from yeast cells, by 
crushing the latter with hydraulic presses and filtering off residual 
cells through porcelain filters. Little or no acid is formed and the 
yeast fermentations are, in general, different in this respect from 
bacterial fermentations in which acid formation, rather than alcohol 
formation, is the prominent feature. 
Fig. 94. — Yeast cells showing budding. 
Structurally, yeasts exhibit greater complexity than the bacteria. 
The cytoplasm of the yeast cell usually exhibits a granular or vacuo- 
lated appearance and nuclear material, or at least structures that 
color like nuclei have been demonstrated. 
The view was formerly held that yeasts had some etiological rela- 
tionship to cancer. Sanfelice^ and others have cultivated organisms 
closely resembling Blastomycetes from cancerous tissue and have 
attempted to harmonize the appearance of the yeasts with certain 
inclusion bodies within cancer cells. The consensus of opinion at the 
present time is wholly against this hypothesis. 
Certain varieties of yeast are definitely known to incite disease in 
man and animals. Busse- isolated a yeast which he called Saccharo- 
myces hominis from a fatal infection in a woman which began in a 
1 Centralbl. f. Bakteriol., orig., 1902, 31, 254. 
2 Ibid., 1894, 16, 175. 
