TISSUES OF THE CONNECTIVE SUBSTANCE. 243 



The fat contained in the fat-cells consists chiefly of triglycerides 

 of stearic, palmitic, and oleic acids. Besides these, especially in the 

 less solid kinds of fat, there are glycerides of caproic, valerianic, 

 and other fatty acids which have not been so closely investigated! 

 In all animal fats there are besides these, as HOFMANX has shown,' 

 free, non-volatile fatty acids, although in very small amounts! 

 Fats from different species of animals, and even from different 

 parts of the same animal, have an essentially different consistency, 

 depending upon the relative amounts of the different fats. In 

 solid fats as tallow tristearin and tripalmitin are in excess, while 

 the less solid fats are characterized by a greater abundance of 

 palmitin and triolein. This last-mentioned fat is found in greater 

 quantities proportionally in cold-blooded animals, and this accounts 

 for the fat of these animals remaining fluid at temperatures at 

 which the fat of warm-blooded animals solidifies. Human fat 

 from different organs and tissues contains, in round numbers, 670- 

 800 p. m. olein. The melting-point of different fats depends 

 upon the composition of the mixtures, and it not only varies for fat 

 from different tissues of the same animal, but also for the fat from 

 the same tissues in various kinds of animals. 



Fat occurs in all organs and tissues of the animal organism, 

 though the quantity may be so variable that a tabular exhibit of 

 the amount of fat in different organs is of little interest. The 

 marrow contains the largest quantity proportionally, having over 

 960 p. m. The three most important deposits of fat in the animal 

 organism are the intermuscular connective tissue, the fatty tissue 

 in the abdominal cavity, and the subcutaneous connective tissues. 



The average composition of animal fat is as follows : C 76.5, 

 H 12.0, and 11.5 per cent. Neutral fats are colorless or yel- 

 lowish and, when perfectly pure, odorless and tasteless. They are 

 lighter than water, on which they float when in a molten condi- 

 tion. They are insoluble in water, dissolve in boiling alcohol, but 

 separate on cooling, often in crystals. They are easily soluble in 

 ether, benzol, and chloroform. The fluid neutral fats give an 

 emulsion when shaken with a solution of gum or albumin. With 

 water alone they give an emulsion only after vigorous and pro- 

 longed shaking, but the emulsion is not persistent. The presence 

 of some soap causes a very fine and permanent emulsion to form 



