200 
PHARMACEUTICAL BOTANY 
usually develops four ascospores. To this order belong Exoascus, 
which is responsible for the abnormal development of tufted masses 
of branches on a number of trees and shrubs, and the yeasts (Sac- 
charomycetaceae) many of which produce fermentation. 
Yeasts are unicellular plants of spheroidal, oval, elliptical, pyriform 
or sausage shape which reproduce by budding. They occur either 
in the wild or cultivated condition and are generally found capable of 
breaking down some form of sugar into alcohol and carbon dioxide. 
According to the kind or kinds of sugar fermented Hansen in 
1888 classified the yeasts as follows: 
1. Species which ferment dextrose, maltose and saccharose: 
Saccharomyces cerevisice I, S. ellipsoideus I, S. ellipsoideus II, 
S. pastorianus I, S. pastorianns II, S. pastorianus III. 
2. Species which ferment dextrose and saccharose, but notmaltose: 
Saccharomyces marxianus, S. exiguus, S. saturnus , S. Ludwigii. 
3. Species which ferment dextrose, but neither saccharose nor 
maltose: Saccharomyces mali Duclauxii. 
4. Species which ferment dextrose and maltose, but not saccharose: 
Saccharomyces n. sp. obtained from the stomach of the honey-bee. 
5. Species which ferment neither maltose, dextrose nor saccharose: 
Saccharomyces anomalies var. belgicus, S. farinosus, S. hyalosporus, 
S. membranif aciens . 
The two most important yeasts in the fermentation industries are 
Saccharomyces cerevisice and Saccharomyces ellipsoideus. 
Saccharomyces cerevisice, commonly called Brewer’s Yeast, is a 
cultivated species with many strains. It is used extensively in the 
brewing and baking industries and in recent years has met with 
considerable esteem by the medical profession in the treatment of 
certain skin diseases. 
When examined under the microscope it is found to be somewhat 
spheroidal to ellipsoidal in outline, 8 to 12/z long, and 8 to 10/z broad. 
It consists of an outer cell wall of fungous cellulose enclosing cyto- 
plasm and a nucleus, the latter invisible without special staining. 
The cytoplasm is differentiated into a clear outer membrane lying 
directly within the cell wall and termed the ectoplasm and an inner 
granular region, the endoplasm. In the young condition of the 
yeast cell numerous glycogen vacuoles are found scattered more or 
