FAT. ' 223 



death. The fat vesicles of the pig are described as being 

 elongated and kidney-shaped. This shape, however, is of 

 rare occurrence, and cannot be regarded as the ordinary 

 and characteristic form, which is most generally more or less 

 spherical or oval. Raspail, observing this exceptional form, 

 was led to institute from it an erroneous comparison between 

 fat vesicles in general and the starch granule. 



Size. The fat vesicles of the adult are usually several 

 times larger than the solid corpuscles of any of the fluids 

 described, the blood, mucus, and milk: the size of the fat 

 vesicles in any given quantity of fat is not uniform ; but, like 

 the globules of milk, varies exceedingly, the dimensions of 

 the larger vesicles surpassing several times those of the 

 smaller. 



One exceedingly interesting law has been observed in re- 

 ference to the size of fat vesicles ; thus it has been ascer- 

 tained that their average magnitude increases from infancy 

 up to adult age : in accordance with this law the fat cells of 

 an infant will be found to be several times smaller than those 

 of a full-grown person, and those of a child again of an in- 

 termediate size. This law will be apparent from an examin- 

 ation of the figures given. (See Plate XVIII.) 



Colour. The colour of fat is subject to considerable 

 variations, but it usually exhibits a tinge, more or less deep, 

 of yellow. The fat of young animals is usually of a lighter 

 colour than that of the full-grown and aged ; this may be 

 seen by a comparison of the fat of an infant with that of an 

 adult, or of the fat of the calf with that of the ox ; in the 

 former it is almost white, while in the latter it frequently 

 exhibits a deep and golden hue. The differences of colour 

 referred to doubtless denote differences in the relative pro- 

 portion of the different constituents of fat. 



In some animals, also, fat of various bright colours is 

 encountered, especially in Birds, beneath the skin of the beak 

 and of the feet ; in the Crustaceae and in some of the Reptilia. 

 In the Triton the fat is of a deep orange colour, approaching 

 to red. The coloration of the iris of birds depends, accord- 



