48 PHYSIOLOGY FOR NURSES 



are rich in protein, starch, fat and salts; while the po- 

 tato is poor, comparatively, in everything but water. 

 Practically the high protein value of the pea is not 

 available while its large percentage of indigestible cel- 

 lulose renders it objectionable when eaten to excess. 



DIGESTION 



That digestion is chiefly a chemical process is per- 

 fectly true; but it involves a process, which may be 

 called vital chemistry, which the test tube has not, and 

 may not, imitate completely. An essential part of di- 

 gestion is carried out by bodies called enzymes or fer- 

 ments. Another is the production, in proper proportion, 

 of the acid or alkali in the presence of which alone 

 these ferments will act ; while yet another is the prepa- 

 ration of food, by chewing, SAvallowing, etc., and its agi- 

 tation in the intestinal canal where it is exposed to the 

 ferments on the one hand and on the other is brought 

 in contact with the vessels by which the products of di- 

 gestion will be carried into the body. 



The Enzymes, or ferments without which food can- 

 not be digested, are of three chief types: (1) amylo- 

 lytic, which convert starch into sugar; (2) fat splitting, 

 which convert fats into glycerin and fatty acids; and (3) 

 proteolytic, or those which convert protein into simpler 

 bodies. 



Besides these there are sugar splitting ferments which 

 change the nonabsorbable into absorbable sugars, and a 

 body which coagulates protein, as in the change of milk 

 to clabber. 



The ferments which act on starchy foods are ptyalin, 

 secreted by the salivary glands, and amylase, formed by 

 the pancreas. 



