PHYSIOLOGICAL CHEMISTRY 



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CHAPTER VI. 

 FATS, FATTY ACIDS, PHOSPHORISED FATS AND CHOLESTEROL. 



THESE bodies are classified together because they are soluble in the 

 same liquids. After extracting an organ or tissue with alcohol, ether 

 or chloroform, and evaporating off the solvent, a more or less syrupy 

 mass is left behind consisting of a varying mixture of the above men- 

 tioned substances. They are often called collectively the lipoids. 



Method for the Extraction of an Organ or Tissue with Ether. The 



simplest method is by means of Soxhlet's apparatus (fig. 225). 

 This consists of an extracting chamber into which opens, 

 near the top, a side tube, connected below with a flask, in 

 which is placed the ether ; above it is connected with a 

 condenser. The flask is placed on a water-bath, and the 

 ether passes into the chamber, and then into the Liebig's 

 condenser, where it is condensed and trickles back into the 

 extracting chamber. The ether thus gradually accumulates 

 in the extraction chamber until it reaches the level of the 

 bend in another side tube opening near the bottom of the 

 extracting chamber, when syphon action is established, and 

 the whole of the ether drains back into the distilling flask. 

 The dried tissue or organ to be extracted is finely ground 

 and placed in a cartridge of porous paper, which is inserted 

 in the extracting chamber. The warm condensed ether as 

 it accumulates in the chamber dissolves out the fat, and 

 carries it into the distilling flask. The process should be 

 allowed to proceed for several hours. The contents of the 

 distilling flask are then removed to a flat dish, and the 

 ether allowed to evaporate. The residue contains the lipoid substances. 



FIG. 225. Soxhlet's. 

 apparatus. 



FATS AND FATTY ACIDS. 



Neutral fats are the ethereal salts of the fatty acids with the tri- 

 atomic alcohol glycerine, and have therefore the general formula : 

 CH 9 -0-CO-X 



C'H 



_ O - CO - X 



CH 2 -0-CO-X. 



They are named according to the fatty acid they contain, thus : stearin, 

 olein. The fatty acids are monobasic organic acids, containing one car- 

 boxylic group (COOH) attached to a hydrocarbon radicle. They belong 

 to two classes, the saturated and the unsaturated. The saturated acids 

 have the general formula C n H 2n+1 . COOH. Those commonly occurring 

 in fats are stearic acid, in which ?i = 17, and palmitic acid, in which 



