254 



Food and its Digestion. 



with the food, exerts upon it a catalytic action, and trans- 

 forms its ingredients into other substances — " Catalysis, 

 (Kara Xuw, I dissolve or decompose), the action of presence 

 in producing decomposition. Catalytic force resolves other 

 bodies into new compounds by mere contact or presence, 

 without itself experiencing any modification." 



The newly formed substances, resulting from this cata- 

 lytic action are absorbed by the vessels, and finally 

 mingled with the general current of the circulation, as 

 blood, by which the system is nourished and sustained. 



The food in order to be digested, is acted upon by no 

 less than five ditferent digestive fluids. 



First, the saliva in the cavity of the mouth. Second, the 

 gastric juice in the stomach. Third, the bile from the liver. 

 Fourth, the pancreatic fluid from the pancreas. Fifth, 

 the intestinal secretions from the follicles in the intestinal 

 canal. 



The saliva acts upon the starchy, carbon and hydrogen 

 elements of the food, converting them into sugar. This 

 action, though not so marked as the action ot the secre- 

 tions further on in the alimentary canal, is one of no little 

 importance, and doubtless some of the forms of indigestion 

 which the physician has to combat in his practice, are a 

 result of the useless expenditure and waste of this secretion 

 in the habit of smoking, and more particularly the habit, 

 almost peculiar to this country, of chewing tobacco. 



The composition of saliva, according to an analysis of 



Bidder and Schmidt, is as follows : 



"Water, » 995.16 



Organic matter, 1.34 



Sulpho cyanide of potassum, , 0.06 



Phosphate of soda, lime, magnesia, 0.98 



Chlorides of sodium and potassium, 0.84 



Mixture of epithelium, 1.62 



1000.00 



The gastric juice acts upon the albumenoid (nitrogen) ele- 



