DIGESTION OP POOD. 



301 



or other proteid matter will be dissolved if it be finely divided 

 and frequently shaken up, so that a greater surface is exposed 

 to the digestive fluid. 



The exact nature of the process by which proteid is changed 

 to peptone is not certainly known. 



Since starch on the addition of water becomes sugar (CoHu 

 Ob + ilaO = OeHuOe), and since peptones have been formed 

 through the action of dilute acid at a high temperature or by 

 superheated water alone, it is possible that the digestion of both 

 starch and proteids may be a hydration ; but we do not know 

 that it is such. 



As already explained, milk is curdled by an extract of the 

 stomach (rennet) ; and this can take place in the absence of all 

 acids or anything else that might be suspected except the real 

 cause; there seems to be no doubt that there is a distinct fer- 

 ment which produces the coagulation of milk which results 

 from the precipitation of its casein. 



• The activity of the gastric ,iuice, and all extracts of the mu- 

 cous membrane of the stomach, on proteids, is due to pepsin, a 

 nitrogenous body, but not a proteid. 



Like other ferments, the conditions under which it is effect- 

 ive are well defined. It will not act in an alkaline medium at 

 all, and if kept long in such it is destroyed. In a neutral me- 

 dium its power is suspended but not destroyed. Digestion will 

 go on, though less perfectly, in the presence of certain other 

 acids than hydrochloric. As with all digestive ferments, the 

 activity of pepsin is wholly destroyed by boiling. 



IN 100 PARTS. 



Water 



Solids 



Bile salts , 



Lecethin, cholesterin 



Pats, soaps 



Mucin and coloring matter 

 Inorganic salts 



Man. 



86-3 



13-7 



7-4 



3-0 

 2-3 



1-1 



Ox. 



90-4 

 9-6 



8'0 



O'S 

 1-3 



Kg- 



88-8 



11-2 



7-3 



3-3 

 0-6 

 1-1 



Fresh. 



95-3 

 4-7 

 3-4 



0-5 

 0-3 

 0-6 



From gall- 

 bladder. 



85'3 

 14-8 

 13-6 



1-3 

 0-3 

 0-6 



The color of the bile of man is a rich golden yellow. When 

 it contains much mucus, as is the case when it remains long in 

 the gall-bladder, it is ropy, though usually clear. Bile may 

 contain small quantities of iron, manganese, and copper, the 



