322 HUMAN PHYSIOLOGY 



food is not great on account of the amount of water they 

 contain. 



They are rich in the potash salts of the organic acids, the 

 importance of which has already been discussed (p. 313). 

 The cellulose forming the walls of the cells in the young 

 and growing part of the leaves seems to be capable of partial 

 digestion in the human intestine. 



Y. Fungi. Mushrooms and other such fungi do not con- 

 stitute a sufficiently important part of the diet to require 

 attention. 



YI. Fruits. These vary considerably in composition. 

 Most are rich in water and carbohydrates, poor in proteids, 

 and contain practically no fat. Their great value lies in the 

 amount of free and combined organic acids they contain. 

 Bananas, which contain about 23 per cent, of soluble carbo- 

 hydrates, may be considered as a food of some import- 

 ance, while dried fruits, especially dates and figs, which 

 contain between 4 and 5 per cent, of proteids and about 

 65 per cent, of carbohydrates, are of considerable nutritive 

 value. 



YII. Nuts. These, unlike the fruits, are for the most part 

 poor in water and carbohydrates but rich in proteids and 

 fats. Chestnuts, however, contain an abundance of carbo- 

 hydrates, and a smaller proportion of proteids and fats. 



Cooking. Few of these food-stuffs are used by civilised 

 man in a raw and unprepared condition. With the object 

 of rendering them more palatable and more easily digested, 

 and also in order to destroy bacteria, they are usually cooked. 

 This process of cooking produces important changes in many 

 of the foods, and its effects must be briefly considered. 



Milk and its products are practically unaltered by cooking. 



Flesh is cooked either by exposing it directly to heat, or 

 by treating it with boiling water. 



Roasting, grilling, broiling, and frying are modifications of 

 the former method, and in all of them the heat at once 

 coagulates the proteids at the outer part of the piece of flesh, 

 and thus forms a more or less impermeable covering, which 

 prevents the escape of the juices of the meat. Hence these 

 methods of cooking, although bringing about a burning of 



