146 



TEXT-BOOK OF PHYSIOLOGY. 



Composition of Animal Foods. The following table shows the 

 average percentage composition of various kinds of meats, cow's 

 milk, and eggs: 



Meats. It will be observed from these analyses that the meats 

 contain from 1 8 to 20 per cent, of a proteid which belongs in virtue 

 of its chemic relations to the group of globulins. In the living con- 

 dition this body, known as myosinogen, is in a semi-fluid condition, 

 but shortly after death undergoes coagulation, giving rise to solid 

 myosin and a soluble albumin. There are also present in meat small 

 percentages of other forms of proteid; e. g., myoalbumin, myoglob- 

 ulin, paramyosinogen, etc. After being subjected to the cooking 

 process, meats contain the albuminoid body gelatin, a product of the 

 transformation of the proteids of the connective tissue. 



The percentage of fat, contained within the meat substance, 

 is very small except in mutton and pork, where it rises to 5.4 per cent, 

 and 5.8 per cent, respectively. The fat-globules in these meats are 

 packed closely between the muscle-fibers, and prevent the easy 

 entrance of the digestive fluids, and hence they are more difficult of 

 digestion than beef. 



The carbohydrates vary from 0.5 to i per cent., and are represented 

 by glycogen. The principal inorganic salts are potassium phosphate 

 and sodium chlorid. 



Cooking, when properly done, not only makes the meat more 

 palatable and appetizing from the development of agreeable flavors, 

 but converts the connective tissue, which, in old animals especially, 

 is tough and resisting, into gelatin, thus rendering it more easy of 

 mastication and digestion. At the same time parasitic organisms, 

 such as the embryonic forms of tenia or tapeworm, trichina 

 spiralis, as well as bacterial growths, which frequently infest the 

 bodies of animals, are destroyed and made harmless. 



Milk is the natural food of the young of all mammals, and is 

 usually regarded as typical on account of , the ratio existing among 

 its nutritive principles. The -analysis given above is that of cow's 

 milk. Examined microscopically, milk is seen to consist of a clear 

 fluid, the milk plasma, holding in suspension an enormous number of 

 small, highly refractive oil globules, which measure on the average 



