146 PHYSIOLOGY. 



Proteid-containing Foods. The principal proteid- 

 containing foods are lean meat, fish, eggs, milk, cheese, 

 and some seeds which abound in the vegetable proteids. 



Meat. Lean meat has about twenty per cent of pro- 

 teid, the rest being chiefly water. Beef and mutton are 

 more easily digested than veal and pork. It is better to 

 buy meat from a very fat animal than from a lean one, for, 

 although there is slightly less proteid in the meat from a 

 fat animal, this loss is more than made up by the addition 

 of fat, which takes the place of water in the meat from a 

 lean animal. There is more nourishment in a round steak 

 than in tenderloin. 



Fish. Fish, when fresh, is a good food. Although, 

 as a rule, salted meats are less easily digested than fresh, 

 salted codfish is a nourishing and economical food. 



Eggs. Eggs contain considerable proteid, but their 

 value as food has been overrated. The yolk has a large 

 amount of fat. Although the egg has all the material 

 needed to form a chick, it is not a perfect food for man. 



Milk. Milk, as we have seen, is an ideal food in that 

 it contains all the kinds of foodstuffs, and in the right pro- 

 portion for the young mammal. But the proportions are 

 not right for the adult. An adult would need four quarts 

 and a half daily, and then he would not get enough carbo- 

 hydrates (represented in milk by the sugar). The oily 

 material in milk is in the form of minute globules, which 

 can easily be seen under the microscope. Each of these 

 oil droplets is supposed to be surrounded by a thin en- 

 velope of albuminous matter, by means of which it is 

 enabled to remain suspended for some time instead of 

 rising quickly to the surface. Such a mixture of oil in a 



