Chemical Constituents of the Animal Body. 187 



organ has the tendency to convert the acids of the ingested 

 fats into other acids with a greater degree of unsaturation 

 (that is, with higher iodine number). The influence of the 

 ingestion of large amounts of various foreign fats on the 

 normal fats from other parts of the animal body have also 

 been investigated by means of the iodine numbers. These 

 experiments form interesting examples of the application 

 of chemical methods to biological research. The following 

 are some examples of iodine numbers : *- 



Beef suet 38-46 



Lard 50-70 



Mutton fat 35-46 



Palm oil 51-5-58-5 



Linseed oil 164-205-4 



Olive oil 79-88 



Butter 26-38 



It is interesting to note the high iodine number of a 

 typical " drying " oil, linseed oil, in the above table. The 

 drying properties (utilized by painters) are no doubt due 

 to the high degree of unsaturation of the fatty acid, by 

 virtue of which the oil readily undergoes oxidation in air 

 to yield solid products. 



(c) The Reichert-Meissl Value. Certain fatty acids 

 obtained by the hydrolysis of fats, such as butyric acid, 

 volatilize readily when distilled in steam. The so-called 

 Reichert-Meissl value denotes the number of c.c. of N/1Q 

 potassium hydroxide which are necessary to neutralize the 

 fatty acids obtainable from 5 grammes of fat, which can 

 be distilled over in steam under certain standard condi- 

 tions of experiment. A small amount of acid passes over 

 with steam, even when the higher non-volatile acids are 

 distilled. Hence the necessity of choosing standard con- 

 ditions. The fat is first saponified with alcoholic potassium 

 hydroxide solution ; the alcohol is evaporated off, the 



