364 PHARMACEUTICAL BOTANY 
gelatinous sheath surrounding the primary wall in some forms. 
Cytoplasm occurs within the cell as well as chromatin, but the 
latter is usually diffused in fine particles through the cell proto- 
plasm and never has been demonstrated to be condensed into a 
definitely organized body called a nucleus. A common method 
of asexual reproduction is possessed by these plants whereby the 
cell cleaves or splits into two parts, each of which becomes a 
separate and independent organism. Sexual reproduction has 
not been conclusively proven, although suspected by some 
investigators. Bacteria occur everywhere but are relatively few 
on high mountain peaks and beneath 3 meters of natural soil. 
They have even been found in the hot geyser springs where no 
other form of life can exist (Thermophilic bacteria). 
According to the various phenomena they produce, they may 
be classified as follows: (a) Zymogens producing fermentation; (b) 
Aerogens producing gas; (c) Photogens producing light; (¢) Chromo- 
gens producing color; (¢) Saprogens, producing putrefaction; (/) 
Pathogens, producing disease; (g) Thermogens, producing heat. 
FERMENTATION, DECAY AND PuTREFACTION.—Fermentation is 
the process which consists of the breaking down of organic sub- 
stances through the action of enzymes produced by living organ- 
isms. ‘The organic substances fermented are various, including 
carbohydrates, proteins and fats. Decay is the fermentation of 
proteins in the presence of oxygen. PurTrEractTIon, although 
frequently used in the sense of the decomposition of proteins, is 
more properly applied to the anzrobic fermentation of proteins, 
many of the products of which possess an offensive odor. When 
carbohydrates undergo fermentation, the products are useful. 
Bacteria cause considerable spoilage of foods and drugs owing to 
their power of producing enzymes. 
BacTERIAL CuLTuREs.—Because of their minute size (a 
space the size of a pinhead may hold eight billion of them), the 
student commences his study of bacterial growths in colonies or 
cultures, each kind possessing characteristics by which they may 
be distinguished and differentiated. These cultures are obtained 
by growing the microorganisms on sterile artificial culture media 
usually in an incubator, the temperature of which is carefully 
regulated to suit the requirements of the organisms grown. The 
