58 



PHYSIOLOGICAL CHEMISTRY* 



FIG. 3. 



SACCHAROMYCES CEREVISI.E, in its quiescent con- 

 dition ; from deposit of beer-yeast, after fermen- 

 tation. 



FIG. 4. 



When yeast is added to a warm solution of glucose, the cells of 



the yeast-plant after a short time 

 begin to multiply by budding. 

 The buds increase rapidly in size, 

 and, when the young cell has be- 

 come nearly as large as its pa- 

 rent, it usually separates and be- 

 gins an independent existence. 

 While in this condition the cells 

 are mostly oval in form, with 

 an average diameter of but 

 little more than 8 mmm. Often 

 two or three are seen con- 

 nected together, forming monil- 

 iform chains. It is by the 

 active growth and development 

 of the cells during this process 

 that the glucose of the solution is 

 decomposed, and alcohol and car- 

 bonic acid produced in its place. 

 Another species of saccharomyces forms the fungus of bread-yeast, 



and a third the ferment of grape- 

 juice, by which it is made to 

 undergo the vinous fermenta- 

 tion. 



When fermentation is used as 

 a test, a little beer-yeast is added 

 to the supposed saccharine fluid, 

 and the mixture kept at the 

 temperature of 25 C. The gas 

 given off during the process is 

 collected and examined, and the 

 remaining fluid is purified by 

 distillation. If the gas evolved 

 be carbonic acid, and if the dis- 

 tilled liquid contain alcohol, there 

 can be no doubt that a ferment- 



SACCHAROMYCES CEKEVISI.E in active germination, able SUgar Was present in the 



From fermenting saccharine solution. yo lution. Glucose undergoes fer- 



mentation more readily and more completely than the other varieties 

 of sugar. 



2. Lactose, C 12 H 24 12 , Sugar of Milk. 



Lactose is the saccharine ingredient of milk, the only fluid in which 

 it is known to occur. It is less freely soluble than glucose, and is less 

 sweet to the taste. In watery solution it rotates the plane of polari- 

 zation to the right 58. 20. In chemical composition it is isomeric with 

 glucose, which it resembles in being decomposed and turned brown by 



