66 HYDROCARBONACEOUS PROXIMATE PRINCIPLES. 



SACCHAEOMYCES OBRKVISI^E during active 

 germination. From fermenting saccharine solu- 

 tion. 



Fig. 7. independent existence. While 



in this active condition the 

 cells are mostly oval in form, 

 and have an average diameter 

 of only a little more than 8 mmm. 

 Often two and three are seen 

 connected together, forming 

 moniliform chains. It is by 

 the active growth and develop- 

 ment of the cells during this 

 process that the glucose of the 

 solution is decomposed, and 

 alcohol and carbonic acid pro- 

 duced 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 un- 

 dergo the vinous fermentation. 



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 about 25 (77 P.). The gas which is given off during the process 

 is collected and examined, and the remaining fluid is purified by distil- 

 lation. If the gas be found to be carbonic acid, and if the distilled 

 liquid contain alcohol, there can be no doubt that a fermentable sugar 

 was originally present in the solution. Glucose undergoes fermenta- 

 tion more readily and completely than most other varieties of sugar. 



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



This is the variety of sugar which is found in milk, the only fluid in 

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

 its sweet taste is less marked. In watery solution it rotates the plane 

 of polarization to the right 58.20. In chemical composition it is 

 isomeric with glucose, which it resembles in several of its reactions, 

 namely, in being decomposed and turned brown by boiling alkalies, in 

 readily reducing the copper-oxide in Trommer's and Fehling's tests, 

 and in undergoing the alcoholic fermentation under the influence of 

 yeast. It enters into fermentation, however, very slowly, as compared 

 with glucose, and the process is usually incomplete. If fermentation 

 go on in the milk itself, or in the presence of other ingredients of the 

 milk, a part of the sugar is converted into lactic acid, C 3 H 6 3 , also a 

 carbo-hydrate. By boiling for ^ome time with dilute sulphuric or 

 hydrochloric acid, lactose becomes readily and completely fermentable. 

 This sugar forms an important element in the food of the young 

 infant, being a constant ingredient of the milk. It is not known 

 from what substance it is formed in the tissues of the mammary gland ; 



