Chap. IX.] NUTRITION AND METABOLISM. 183 



There are two kinds of metabolism. In one the new mole- 

 cules formed are more complex and more unstable than those out 

 of which they are formed. This is termed anabolism, and the 

 intermediate substances which may be formed during the process 

 are called anastates. The process involves the storing up of 

 energy. In the other the new molecules are less complex and 

 less unstable than those out of which they are elaborated. It is 

 called katabolism, the intermediates being termed Jcatastates, 

 The process involves the setting free of energy in the form of 

 heat or visible motion. It is under this latter category that the 

 processes of secretion fall. They are katabolic processes, and 

 the mother of mucin and mother of ptyalin are katastates. On 

 the other hand the conversion of dextrin into glucose is an 

 anabolic process, the molecule of sugar being more complex than 

 that of dextrin, while maltose, as an intermediate substance, is 

 an anastate. 



The product of the cardiac and pyloric glands of the stomach 

 is gastric juice. The fluid is strongly acid (HC1), and contains 

 the ferment pepsin, with small quantities of a rennet ferment. 

 The ferments may be extracted from the minced mucous mem- 

 brane of the stomach with four or five times its bulk of glycerine, 

 which should be allowed to act for some days. The fluid may then 

 be strained off through muslin, and added to from ten to twenty 

 times its volume of dilute (*2 per cent.) hydrochloric acid. Such 

 artificial gastric juice will be found to have no action on starch 



If, however, some chopped white of egg or meat be placed in 

 the solution, and be kept in the warm (38C.), the white of egg 

 will be dissolved, and of the meat only a pulp of connective 

 tissue and fatty matter will remain. And if some of the solution 

 be carefully neutralised and added to fresh milk, the milk will 

 clot, owing to the coagulation by the rennet ferment of casein, 

 which will dissolve through the action of the pepsin if the 

 solution be again acidified and placed in the warm. . 



Whereas saliva, therefore, has the property of converting 

 starch into sugar, gastric juice has the property of converting 

 proteids (e.g. albumin, fibrin, myosin, casein), and such nitro- 

 genous materials as gelatin and chondrin, into bodies called 



