TISSUES OF THE CONNECTIVE SUBSTANCE. 247 



the residue is dissolved in water and shaken with ether, which dis- 

 solves the cholesterin. The fatty acids are separated from the 

 watery solution of the soaps by the addition of a mineral acid. If 

 a mixture of soaps, neutral fats, and fatty acids is originally present, 

 it is treated first with water, then agitated with ether free from 

 alcohol, which dissolves the fat and fatty acids, while the soaps 

 remain in the solution, with the exception of a very small amount 

 which is dissolved by the ether. 



To detect and to separate the different varieties of neutral fats 

 from each other it is best first to saponify them with alcoholic 

 potash. After the evaporation of the alcohol they are dissolved in 

 water and precipitated with sugar of lead. The oleate of lead is 

 then separated from the other two lead-salts by repeated extraction 

 with ether. The residue insoluble in ether is decomposed on the 

 water- bath with an excess of soda solution, evaporated to dryness, 

 finely pulverized, and extracted with boiling alcohol. The alcoholic 

 solution is then fractionally precipitated by barium acetate or 

 barium chloride. In one fraction the amount of barium is deter- 

 mined, and in the other the melting-point of the fatty acid set free 

 by a mineral acid. The fatty acids occurring originally in the ani- 

 mal tissues or fluids as free acids or as soaps are converted into 

 barium salts and investigated as above. 



The derivation of the fats in the organism may occur in various 

 ways. The fat of the animal body may consist partly of absorbed 

 fat of the food deposited in the tissues and partly of fat formed in 

 the organism from other bodies, such as albuminous bodies or 

 carbohydrates. 



That the fat of the food which is absorbed in the intestinal 

 canal may be retained by the tissues has been shown in several 

 ways. LEBEDEFF and MUNK have fed dogs with various fats, such 

 as linseed-oil, mutton-tallow, and rape-seed-oil, and have afterwards 

 found the administered fat in the tissues. HOFMANN starved dogs 

 until they appeared to have lost their fat, and then fed them upon 

 large quantities of fat and only little proteids. When the animals 

 were killed he found so large a quantity of fat that it could not 

 have been formed from the administered proteids alone, but the 

 greatest part must have been derived from the fat of the food. 

 PETTENKOFER and VOIT arrived at similar results in regard to the 

 behavior of the absorbed fats in the organism, though their experi- 

 ments were of another kind. MUNK has found that on feeding 

 with free fatty acids, these are deposited in the tissues, not, how- 



