FERMENTATION AND GERM DISEASES 65 



extremely harmful. When substances like meats are fer- 

 mented (or putrefied) deadly poisons are sometimes pro- 

 duced. Hence, materials that were originally wholesome and 

 harmless may, through fermentation, become unwholesome 

 or even poisonous. 



In the study of physiology we are concerned with both 

 the organized and the unorganized types of ferments, but in 

 consideration of digestion we have to do especially with the 

 latter, or enzyme type. Several enzymes are formed in the 

 body. Saliva contains one, which is called ptyalin. The gas- 

 tric juice contains a second, called pepsin and another, called 

 rennet. The pancreatic fluid probably contains three, 

 trypsin, amylopsin and steapsin, all of which contribute to 

 the digestion of food. They are all normal products and are 

 secreted by glands. 



Organized ferments are living organisms, capable of growth 

 and multiplication. Because of their microscopic size they 

 are frequently called microbes; they are also called germs; 

 but neither of these terms is very satisfactory, and it is better 

 to call them by their proper names, yeasts and bacteria. 



Living ferments, save when taken in large numbers, are 

 invisible to the naked eye but are easily seen with a microscope. 

 They differ from each ^_^^ _^ ^-NX~X 



other chiefly in their ()( )( ) ( Y J 



method of multiplica- ^^ 

 tion. Yeasts multiply 

 by the formation of 

 a small bud on the <r I_ID 



side of the plant; Fig. FlG - 28. SHOWING THE METHOD OF 

 27. The bud grows in MULTIPLICATION OP BACTERIA, BY 



. . SIMPLY ELONGATING AND THEN DIVID- 



size until finally it is ING 

 as large as the original 



plant, when it may break away as a separate one. Bac- 

 teria, however, simply increase a little in length and then 

 break irx two in the middle; Fig. 28. Both bacteria and 



