THE CHEMISTRY OF BACTERIA. 85 



liberated on the death of the cell. Moreover, the outward 

 diffusion of the toxin is favored by certain conditions which 

 are, as yet, but imperfectly understood. 



The toxins are very unstable chemical compounds. 

 They are weakened, or destroyed by heat, light, exposure 

 to oxygen and by various chemical reagents. 



Ferments. As a rule, a substance in order to be util- 

 ized as a food must be brought into solution. The starch 

 present in bread, or in the potato, is insoluble in water and 

 consequently would be valueless to an animal if the latter 

 did not possess some means of splitting up the starch 

 molecule and thus bringing its constituents into solution. 

 The saliva and the pancreatic secretion contain soluble, 

 starch-splitting ferments which act upon starch and con- 

 vert it into sugar. The sugar can now be readily absorbed 

 and utilized by the animal organism. A hard boiled egg, 

 or a piece of meat, consists chiefly of protein or albuminous 

 matter, which is practically insoluble. As long as it is in 

 this insoluble condition it cannot be absorbed by the living 

 organism and utilized as food. It is well known, however, 

 that the hardest egg and toughest meat can be readily dis- 

 solved by the aid of the protein-splitting ferments con- 

 tained in the gastric and pancreatic secretions. The fats 

 can be absorbed directly, when in a very finely divided 

 condition. The formation of an emulsion is necessary and 

 this is brought about by the fat-splitting ferment of the 

 pancreatic juice. 



It is evident, then, that in the case of the animal the 

 cells of the salivary gland, of the stomach, and of the pan- 

 creas produces certain soluble substances known as fer- 

 ments or enzymes. These ferments are necessary to the 

 preparation of the food for absorption and without their 

 aid, it is safe to say, the animal could not exist. What is 

 true of the higher form of life is equally true of lower forms. 

 When bacteria are planted on coagulated egg albumin, or 



