120 HUMAN PHYSIOLOGY 



beef soup) there are, excepting the floating fat droplets and a 

 little gelatin, no combustible foodstuffs and it can therefore not 

 be regarded as a strengthening food. It contains besides the salts 

 (potassium phosphate) the extractives (kreatin, xanthin) which 

 impart to it a delicious flavor and a stimulative activity. It is 

 only a condiment. 



Besides the beef of muscle, other animal organs are used as food; 

 some of these also contain large quantities of proteids and gelatin. 



Human milk contains more sugar but less proteids and salts 

 than cow milk. To render cow milk like human milk (which is 

 necessary for the nursing child), it must be diluted with water and 

 lactose must be added. 



The chief proteid of milk is caseinogen. The caseinogen of 

 cow milk is coagulated by rennin in larger flakes than that of 

 human milk and is therefore less accessible to the action of the 

 digestive fluids. Hence children frequently cannot use cow milk. 

 This difference in coagulation is not due to any chemical differ- 

 ence in the caseinogen, but to the different amounts of calcium 

 salts present in the milk. 



The calcium salts of milk are used to build up the skeleton of 

 the growing organism. 



The cream which rises to the top when milk stands, or which 

 can be centrifugal ized from milk, furnishes butter. The butter is 

 obtained by beating the cream which breaks the caseinogen 

 pellicles of the fat globules so that the fat globules flow together. 



Unsalted butter consists chiefly of fat, 90$, mainly glycerides 

 of oleic, palmitic, and stearic acids and, in smaller quantities, of 

 butyric, caproic, and caprylic acids; it further contains 8$ water 

 and casein (2$), lactose and salts. The buttermilk which is left 

 can still be regarded as good food, as it contains much proteid 

 (3-4$) and sugar (4$). 



When milk is coagulated by rennin, cheese (casein coagulate) 

 is formed; the residue is called whey. The casein incloses the 

 fat globules, and after the whey has been removed it undergoes a 

 putrefactive process, the ripening of cheese. By this process part 

 of the proteids. are peptonized, part are decomposed into amido 

 acids; besides this, fatty acids are set free. Cheese is a valuable 

 food because it contains much proteid and fat. Fat cheese con- 

 tains 25$ proteid and 30.5$ fat; poor cheese contains 34$ proteid 

 and 1 1.5$ fat. 



The white of egg contains only egg albumin; the yolk of egg 

 contains, besides the proteids (vitellin), chiefly fat, lecithin, and 

 cholesterin. 



All vegetables contain a substance not found in the animal 

 food cellulose or wood fibre. This is but slightly or not 



