156 ANATOMY AND PHYSIOLOGY 



concentration of waste matters in too small bulk for the action of 

 the large intestine. Three reasons for cooking food are as follows : 



Cooked starch is more easily digested than raw, for the following 

 reasons: The change of starch into sugar requires that it should 

 first be hydrated, that is, combined with water. It exists in gran- 

 ules and each granule of starch has a covering of cellulose which is, 

 in saliva, indigestible. In the process of cooking, the boiling 

 water penetrates to the granule, uniting with it and causing it to 

 free itself from the envelope. At once it can be acted upon by 

 ptyalin if in the mouth, or amylopsin if in the small intestine. 

 With raw starch, hydration goes on slowly or not at all. Imper- 

 fectly cooked starch is unwholesome for the same reason. 



Vegetables also should be thoroughly cooked both on account 

 of the starch which they contain, and the fibrous material, which 

 needs partial disintegration by heat. 



Meats are more easily digested if cooked long enough to soften 

 their connective tissue fibers. By heat these are converted into 

 a gelatinous substance which can be disposed of by pepsin and 

 trypsin. 



Another advantage secured by the cooking of food, lies in the 

 effect of the flavors thus developed, by means of which appetite 

 is encouraged and the secretion of digestive fluids is stimulated. 



Clinical note. The "scraped beef sandwich," so of ten ordered for patients, 

 contains the substance of the muscle cell alone, which has been scraped away 

 from the connective tissue fiber; it is easily digestible because it may at once 

 be converted into peptone without the necessity for first digesting the tougher 

 covering. 



DIGESTION 



Digestion is the process of so changing the food in the 

 alimentary canal that its nutritive parts may be absorbed into the 

 system. 



The organs described in Chapter VIII are so connected and 

 arranged that they receive and act in consecutive order upon the 

 food, causing a series of changes which result in separating nutri- 

 ment from waste and preparing it for absorption, expelling the waste 

 from the system. 



The process of digestion begins in the mouth and continues 

 throughout the small intestine. The food is first divided into 



