224 THE SOLIDS. 



ing to Wagner, upon a fat which is accumulated in drops, and 

 perhaps also in cells. 



Consistence. The consistence of fat is different in different 

 animals, and also varies in accordance with the temperature ; 

 thus the fat of the pig is softer than that of the ox or sheep ; 

 that of the human subject is intermediate between both in its 

 consistence, and all kinds of fat are harder in cold than in 

 warm weather. The variation in the solidity of fats depends 

 upon the amount of stearine and elaine which they contain ; 

 the hard fats containing a greater quantity of stearine than 

 the soft fats, in which the elaine is greatest. 



Structure. Most observers agree in assigning to each fat 

 vesicle a distinct investing membrane, notwithstanding 

 which fact the proofs adduced by them of the existence of such 

 a structure are by no means so decisive as to render such a 

 conclusion anything more than doubtful : thus micrographers, 

 hitherto have been unable to demonstrate the presence 

 around normal fat vesicles of an enveloping tunic, but have 

 been contented to rest their opinion upon the indirect and 

 uncertain evidence to be derived from a knowledge of the 

 action of re-agents ; upon testimony, in fact, analogous to 

 that upon which Henle and Mandl decided in favour of the 

 existence of a membrane surrounding the milk globule. 



Schwann, indeed, states that he found the membrane of 

 the fat cell to be almost as thick as the blood globule of man 

 in an infant affected with mollities ossium.* 



Henle also has observed around the obscure periphery of 

 a fat cell a strait and clear band, but could not assure him- 

 self that this was not the result of an optical illusion.f 



The above are the only trustworthy observations of a 

 direct character recorded in proof of the existence of a dis- 

 tinct tunic to the fat vesicle, and they are evidently not of a 

 satisfactory or decisive nature. 



The indirect testimony procured from a knowledge of the 

 action of re-agents is as follows : Ether is stated to render 



* Mikroskopische Untersuchungen, p. 140. 

 t Anat. Gen. p. 422. 



