CHEMISTRY OF ANIMALS. 6^ 



termined in a thoroughly satisfactory manner. Fats occur 

 in most animal tissues and fluids, and in many cases they 

 are certainly not unnecessary or superfluous constituents. 

 There can also be no doubt but that the fats are largely 

 instrumental in maintaining the temperature of the body. 



The nitrogcTWi^^ compounds of animals are numerous, but 

 the three most important are albumen, fibrine, and caseine. 



Album€7i is a compound of carbon, hydrogen, oxygen, 

 nitrogen, and sulphur, but in its soluble form it is combined 

 with some salt of sodium. In its soluble state, albumen is 

 a colourless, tasteless, glairy fluid, which *' coagulates " or 

 becomes solid at a temperature of about 150° Fahr., is pre- 

 cipitated by all the mineral acids (except tribasic phos- 

 phoric acid), and is not precipitated by any of the vegetable 

 acids (except tannic acid). Albumen is also thrown down 

 from its solutions by alum, corrosive sublimate, sulphate of 

 copper, acetate of lead, creasote, and alcohol- Albumen is 

 found in the blood, and in most of the animal fluids, and 

 also in some tissues ; and white of tg% is almost wholly 

 composed of it. 



Fibrine is very closely allied to albumen, and is best 

 known as occurring in a fluid form in the blood. It also 

 occurs, in a slightly modified state, in muscle. It has the 

 power, when removed from the body, and sometimes whilst 

 still within the body, of spontaneously solidifying or coag- 

 ulating. When coagulated, it is almost undistinguishable 

 chemically from coagulated albumen. 



Caseine is an albuminous body which occurs abundantly 

 in milk. It differs from albumen in not being coagulated 

 by heat alone, but in being precipitated from its solutions 

 by acetic acid. 



The eminent chemist Mulder held the opinion that albu- 

 men, fibrine, and caseine, with the similar bodies found in 

 vegetables, are compounds of a substance which he named 

 " proteine " with sulphur and phosphorus. He further 

 believed that "■ proteine " consisted of the four essential 



