THE DIGESTION OF FOOD 93 



paratively clear liquid. A chemical examination of these 

 preparations will reveal the fact that the compomids of 

 the meat are present in solution in somewhat modified 

 forms, and that the starch has been changed to a sugar 

 or other soluble bodies. In both cases substances insolu- 

 ble in water have become soluble and diffusible. 



129. Enzyms and their action. — ^The cause of these 

 changes is the presence, one in the pig's stomach and one 

 in the malt, of ferments of the enzym class, the former of 

 which renders proteins soluble, the latter producing a 

 similar result with the insoluble carbohydrates. This 

 action is not entirely like that caused by the presence of 

 the organized ferments, where oxidation occurs in many 

 cases. The enzyms simply induce the proteins and starch 

 to take up the elements of water, a change which is termed 

 hydrolysis. How this is done cannot be explained in 

 simple terms, if at all. Our knowledge of the manner of 

 the change rests to some extent upon theoretical grounds. 

 Enzyms are regarded as catalyzers, that is, compounds 

 which by their presence cause chemical changes while 

 they themselves do not enter into the combinations 

 formed. A small quantity of an enzym may cause changes 

 in a large amount of material, the enzym itself under- 

 going no appreciable change. The digestion of food is 

 largely accomphshed through the specific effect of enzyms, 

 of which every digestive fluid contains one or more. Exam- 

 ples of these are the pepsin and pancreatin of the drug- 

 store that contain enzyms mixed with more or less of 

 impurities. The various enyzms are often given names 

 according to their function: invertase, which inverts or 

 splits sucrose; glucose, that changes any carbohydrate 

 into glucose (also called maltase); lactase, that splits lac- 

 tose into simpler sugars. In general, the ferments acting 



