46 PHYSIOLOGY FOR NURsi.S 



Fats, \vluMi boiled with soda or potash, break up into 

 glycerin and fatty acids, which latter combine with soda 

 or potash and form soap. 



If fats, soap and water be thoroughly shaken together 

 the fat breaks up into small particles which are held in 

 suspension in the water forming an emulsion. Milk is 

 an excellent emulsion whose fat gradually rises to the 

 top in the form of cream. 



Nitrogenous Bodies. The chief constituents of mus- 

 cles, glands, nervous tissue, serum, blood and lymph are 

 complex bodies called proteins. They occur in vegeta- 

 bles as well as in animals, but much vegetable protein 

 is indigestible by human organs and comes to us only 

 after furnishing food for the lower animals. Thus peas 

 and beans contain 23.7 per cent protein as compared 

 Avith 22.7 in fowls and 20 per cent in beef; but so much 

 of the protein of peas is unusable by the human diges- 

 tive organs, that this vegetable can not be used as a sub- 

 stitute for meat. Various names are employed to desig- 

 nate the protein derived from different sources. One 

 found in milk or cheese is called casein; that in the yolk 

 of eggs vitellin and that in muscle either myosin, or 

 sj/ntonin. 



Not all bodies which contain nitrogen are capable of 

 maintaining health. The familiar body called gelatin, 

 derived from the skin and connective tissue, contains a 

 considerable proportion of nitrogen and yet an animal 

 fed upon it alone will starve almost as quickly as one 

 deprived of food entirely. This seems to be due to the 

 absence of certain amino bodies which are formed of 

 nitrogen and hydrogen in the proportion of one part of 

 N to two of H or NH 2 . That it is the absence of these 

 amino bodies, or amino acids, which keeps gelatin 

 from maintaining a nitrogen balance, is proved by feed- 



