298 



THE TISSUES. 



Fi S- 189 - In the emaciated subject scarcely any nor- 



mal fat-cells are met with ; but this topic will 

 be resumed in the last subdivision of this 

 chapter. 



Peculiarities in the Lower Animals. 



Fat cells do not exist in the invertebrata, 

 though fat-globules do (p. 73), and often in 

 great abundance. There is, therefore, in 

 Fat-ceiis with crystals of them no true adipose tissue. The larvae of 

 margaric acid. a. Ceii with i nsec t s contain a large amount of fat-glo- 



a star of crystalline needles, -i 

 as they may be found not un- DUieS. 



commonly in normal fat. b. The fat-cells of the pig are generally some- 

 ceii quite filled with crystals, w h a t kidney-shaped. In birds, they are 



are^aLTeTsut^-Ma:- smaller than mm > A often contain a 

 nified 350 diameters. (KoUi- bright colored fluid ; e. g. the bright colors 

 ker -) about the beak, and of the legs in some spe- 



cies, are said to depend on layers of cells 



beneath the skin containing colored fat. The bright colors'of cer- 

 tain crustaceans and reptiles, are also due to a similar cause, when 

 not dependent upon pigment-cells. Wagner believes that the color 

 of the iris in birds is also due to a deposit of fat. 



The fat of different animals presents four varieties, so far as its 

 density after death is concerned ; viz., oil, lard, tallow, and sperma- 

 ceti the first containing the most oleine, and the last the most 

 stearine. The fat of the bear does not congeal at ordinary tempe- 

 ratures, i. e. it remains an oil; and hence its value to perfumers. 

 Lard is obtained from the hog; tallow from the ox, sheep, &c., 

 and spermaceti from cavities in the cranium of the whale. Human 

 fat is intermediate in density between lard and tallow. The fat 

 upon the omenturri of the sheep is called suet. 



Chemical Composition of Adipose Tissue. 



This includes, (1) the composition of the fluid fat itself; (2) that 

 of the walls of the fat-cells; and (3) of the intercellular areolar 

 tissue. 



1. If adipose tissue be exposed to a high temperature the fat- cells 

 burst, and the fat escapes ; the cell-walls and the areolar tissue form- 

 ing a solid residue. It has already been shown that the fat consists 

 of oleine, stearine, and margarine; and their composition has been 

 specified on page 76. 



2. The composition of the cell- wall is not precisely known ; but 

 there is no room to doubt that it is an albuminous compound. 



