ii6 



PHYSIOLOGY. 



pand greatly. This causes the bread to "rise" more, and baked in 

 this condition it is ''Hght." There are two special processes accom- 

 panying the fermentation by yeast: ist, the evolution of carbon dioxide 

 as shown above; and, 2d, the formation of alcohol. The best illus- 

 tration of this second process is the brewing of beer, where a form of 

 the same organism which is employed in "bread rising" is used to "brew 

 beer." 



237. The yeast plant. — Before the caustic potash is placed in the tube 

 some of the fermented liquid should be taken for study of the yeast plant, 

 unless separate cultures are made for this pur- 

 pose. Place a drop of the fermented liquid 

 on a glass slip, place on this a cover-glass, and 

 examine with the microscope. Note the min- 

 ute oval cells wdth granular firotoplasm. These 

 arc the veast plant. Note in some a small 

 "bud" at one side of the end. These buds 

 increase in size and separate from the parent 

 plant. The yeast plant is one celled, and 

 multiplies by "budding" 

 or "sprouting." It is c 

 fungus, and some species 

 of yeast like the present 

 one do not form any my- 

 celium. Unrlcr certain 

 conditions, which are not 

 very favorable for growth 

 (example, when the yeast is 

 grown in a weak nutrient 

 ngie substance on a thin layer 



Fig. 108. 

 Fermentation tube filled 

 with CO2 frf)m actiiin of 

 yeast in a sugar solution. 



Fig. 1 08a. 

 Yeast. Saccharo- 

 myces cerivisese. a. 

 small colony; b, single 

 cell budding; 



cell forming an ascus c „ 1 » P.,ris slah"l 

 with four spores; d. °' ^ plaster tans slaD), 

 spores free from the several spores are formed 

 ascus. (After Roes.) 



in many of the veast cells. 

 After a period of rest these spores. will sprout and produce the yeast plant 

 again. Because of this peculiar spore formation some place the yeasi 

 among the sac fungi. (See rhissification of the fungi.) 



238. Organized ferments and unorganized ferments. — An organism 

 like the yeast plant which produces a fermentation of a liquid with evo- 

 lution of gas and alcohol is sometimes called a jeyuwul, or jiruioit or- 

 ganism, or an orgntiiccd ferment. On the other hand the diaslalic fer- 

 ments or enzymes like diastase, taka diastase, animal dia.stase (ptyalin in 

 the saliva), cytase, etc., are unorfianizrJ fernienls. In (he ease of these 

 it is better to say enzyme and leave the word ferment for the ferment 

 organisms. 



