482 APPLIED BIOLOGY 



404. Effect of Cooking Foods. Cooking not onl/renders 

 foods more palatable, but also more digestible. It is easily 

 observed that meats and vegetables are softened by cooking 

 processes, and this aids the penetration of digestive juices. 

 See effect of boiling upon starch ( 398) . Roasting, broiling, 

 boiling, and steaming best prepare foods for digestion; 

 while frying in lard, butter, or oil causes the oily materials to 

 penetrate the food and thus render the penetration of diges- 

 tive juices more difficult. In general, a similar result comes 

 from any heating of starch and fat together; and hence 

 pastries, such as pie-crust, are more indigestible than would 

 be the same amount of the ingredients taken into the stomach 

 without heating together. Various methods of making 

 starchy foods porous, such as the action of baking-powder 

 and yeast, favor rapid penetration by the digestive juices. 



405. Transportation of Digested Food to All Cells. It 

 has been slated in a general way that foods are required by 

 all the living cells of the human body. The study of diges- 

 tion and absorption has shown how foods get into the blood, 

 and now we want to know how foods get from the blood into 

 the cells. This requires (1) that blood should be moved 

 from the capillaries in the walls of the digestive organs to 

 the capillaries in all the other organs of the body, and (2) then 

 absorption from the blood by cells which need food. Before 

 one can understand how food is transported to all parts of 

 the body, it is necessary to make some study of the general 

 plan of structure of the organs concerned with the move- 

 ment of blood and lymph, and also of the nature of these 

 two liquids. Hence our next lesson deals with these topics. 



BLOOD AND LYMPH 



406. Structure of Blood. If examined with the micro- 

 scope, blood is found to be a liquid, called plasma, in which 

 float numerous small bodies, blood-corpuscles or blood-cells. 



