178 PHYSIOLOGICAL CHEMISTRY 



and stearin, the percentage of any one of these fats present depending 

 upon the particular species of animal from whose tissue the fat was 

 derived. Thus the ordinary mutton fat contains more stearin and less 

 olein than the pork fat. Human fat contains from 67 per cent to 85 per 

 cent of olein and, according to Benedict and Osterberg, upon analysis 

 yields 76.08 per cent of carbon and 11.78 per cent of hydrogen. Butter 

 consists in large part of olein and palmitin. Stearin, butyrin, caproin 

 and traces of other fats are also present. 



Pure neutral fats are odorless, tasteless, and generally colorless. 

 They are insoluble in the ordinary protein solvents such as water, salt 

 solutions, and dilute acids and alkalis, but are very readily soluble in 

 ether, benzene, chloroform, and boiling alcohol. The neutral fats are 

 non-volatile substances possessing a neutral reaction. If allowed to 

 remain in contact with the air for a sufficient length of time they become 

 yellow in color, assume an acid reaction and are said to be rancid. The 

 neutral fats may be crystallized, some of them with great facility. The 

 crystalline forms of some of the more common fats are reproduced in 

 Figs. 50, 51 and 52 on pages 176, 179 and 181. Each individual fat 

 possesses a specific melting- or boiling-point (according to whether the 

 body is solid or fluid in character) , and this property of melting or boiling 

 at a definite temperature may be used as a means of differentiation in 

 the same way as the coagulation temperature (see page 105) is used for 

 the differentiation for coagulable proteins. When shaken with water, 

 or a solution of albumin, soap, or acacia, the liquid fats are finely divided 

 and assume a condition known as an emulsion. The emulsion with 

 water is transitory, while the emulsions with soap, acacia, or albumin 

 are permanent. 



The fat ingested continues essentially unaltered until it reaches the 

 intestine where it is acted upon by pancreatic lipase (steapsin) , the fat- 

 splitting enzyme of the pancreatic juice (see page 188), and glycerol 

 and fatty acid are formed. The glycerol is absorbed directly. The 

 fatty acid thus formed unites with the alkalis of the pancreatic juice 

 and forms soluble soaps. These soaps are readily absorbed. That 

 bile is of assistance in the absorption of fat is indicated by the 

 increase of fat in the feces when for any reason bile does not pass 

 into the intestine. Bloor 1 claims that neither petroleum hydrocar- 

 bons nor nonsaponifiable esters, e.g., wool fat (lanolin), are absorbed. 

 He believes that saponification is a necessary preliminary to absorption. 



The fat distributed throughout the animal body is formed partly 

 from the ingested fat and partly from carbohydrates and the " carbon 



1 Bloor: Jour. Biol. Chem., 15, 105, 1913. 



