ADIPOSE TISSUE. 159 



iey become somewhat polyhedral, from the flattening of their walls 

 against each other. Their intervals are traversed by a minute net-work 

 of blood-vessels (Fig. 37), from which they derive their secretion ; and 

 it is probably by the constant moistening of their walls with a watery 

 fluid, that their contents are retained without the least transudation, 

 although they are quite fluid at the temperature of the living body. If 

 the watery fluid of the cell-walls of a mass of Fat be allowed to dry up, 

 and it be kept at a temperature of 100, the escape of the contained oily 

 matter is soon perceptible. By this provision, the fatty matter is alto- 

 gether prevented from escaping from the cells of the living tissues, by 

 gravitation or pressure ; and as it is not itself liable to undergo change 

 when secluded from the air, it may remain stored up, apparently unal- 

 tered, for almost an unlimited period. 



259. The consistency, as well as the Chemical constitution, of the 

 fatty matter contained in the Adipose cells, varies in different animals, 

 according to the relative proportions of three component substances 

 which may be distinguished in it, Stearine, Margarine, and Oleine. 

 The two former are solid when isolated, and the latter is fluid ; but at 

 the ordinary temperature of the warm-blooded animal, they are dissolved 

 in it. Of these, Stearine is the most solid ; and it is the most largely 

 present, therefore, in the hardest fatty matter, such as mutton-suet. It 

 is crystalline like spermaceti ; it is not at all greasy between the fingers, 

 and it melts at 143. It is insoluble in water, and in cold alcohol and 

 ether : but it dissolves in boiling alcohol or ether, crystallizing as it 

 cools. The substance termed Margarine exists along with stearine in 

 most fats, but it is the principal solid constituent of Human fat, and 

 also of Olive oil. It corresponds with Stearine in many of its proper- 

 ties, and is nearly allied to it in Chemical composition ; but it is much 

 more soluble in alcohol and ether, and it melts at 118. On the other 

 hand, Oleine, when pure, remains fluid at the zero of Fahrenheit's ther- 

 mometer ; and it is soluble in cold ether, from which it can only be 

 separated by the evaporation of the latter. It exists in small quantity 

 in the various solid fats ; but it constitutes the great mass of the liquid 

 fixed oils. The tendency of these to solidification by cold, depends upon 

 the proportion of stearine or margarine they may contain. 



260. All these substances are neutral compounds formed by the union 

 of SteariCy Margaric, and Oleic acids, respectively, with a base termed 

 Glycerine ; this base may be obtained from any fatty matter, by treat- 

 ing it with an alkali, which unites with the acid 'and forms a soap, 

 setting free the Glycerine. They contain no Nitrogen ; and their pro- 

 portion of Oxygen is extremely small in comparison with their amount 

 of Carbon and Hydrogen : thus Stearine has 142 Carbon and 141 Hy- 

 drogen to 17 Oxygen : and in the other substances the proportions are 

 similar. The fatty bodies appear to be mutually convertible ; thus mar- 

 garic acid may be procured from stearic acid, by subjecting it to dry 

 distillation : and there is ample evidence that animals supplied with one 

 of them may produce the others from it. 



261. Since these Fatty matters are abundantly supplied by the Vege- 

 table kingdom, and are found to exist largely in substances which were 

 not previously supposed to contain them, it is not requisite to suppose, 



