252 
PHARMACEUTICAL BOTANY 
4. Species which ferment dextrose and maltose, but not saccha¬ 
rose: Saccharomyces n. sp. obtained from the stomach of the honey¬ 
bee. 
5. Species which ferment neither maltose, dextrose nor saccharose: 
Saccharomyces anomalus var. belgicus, S. farinosus, S. hyalosporus, 
S. membranifaciens. 
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 12^4 long, and 8 to 10^ 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 
less uniformly throughout this region but as the cell matures these 
coalesce, until, in a very old cell, a huge glycogen vacuole may be seen 
occupying most of the interior, with the cytoplasm and nucleus 
pushed up against the cell wall and forming there a very narrow 
layer. 
Yeast plants grow in dilute saccharine solutions containing dis¬ 
solved nitrogenous substances such as beerwort, Pasteur’s solution, 
grape juice, etc. Here they are constantly wasting away and as 
constantly being built up. The question may well arise: “How do 
they obtain the material necessary for growth and repair?” The 
answer, in a general way, is not difficult. The fluid in which they 
live is a solution of sugars and of nitrogenous and other matters. 
The cell walls are readily permeable. Food substances diffuse 
through it into the cell, and by a series of changes (which, indeed, 
it is no easy matter to understand) are converted into new living 
substance. The waste products likewise diffuse readily outward. 
