222 THE SOLIDS. 



ART. VIII. FAT. 



THE transition from the fluids to the solids would appear to 

 be a very easy and natural one through the substance about 

 to be described : thus fat bears an evident relation to both 

 the former and the latter, remaining during life in a soft and 

 semi-fluid state, and after death becoming hard and solid ; 

 it is, however, to the milk globules amongst the fluids that it 

 manifests the closest affinity, the fat vesicles, especially those 

 of early life, and the milk globules resembling each other in 

 form, in appearance, and in the manner in which re-agents 

 act upon them. 



Fat is made up of the aggregation of a number of globules 

 or vesicles, which some deem to be true cells, and which are 

 held in juxta-position by intersecting bands of cellular tissue; 

 these vesicles have a smooth surface, semi-opaque texture, 

 and they reflect the light in the strongest manner. 



Contents. The contents of fat vesicles usually present a 

 homogeneous appearance, sometimes nevertheless, as when 

 undergoing decomposition, and when they have been subjected 

 to pressure, they exhibit a granular aspect ; these contents 

 are of an oily nature, and chemists have detected in the lard 

 of the pig the organic products, oleaine, stearine, margaric 

 acid, a yellow colouring matter having the odour and the 

 nauseous taste of bile, and the chemical salts, chloride of so- 

 dium, acetate of soda, and traces of carbonate of lime and 

 oxide of iron. It is probable that of these constituents the 

 presence of the chloride of sodium depended on the mode of 

 preparation of the lard. 



Form. The form presented by the fat vesicles is various, 

 but is usually either globular, oval, or polygonal. The first 

 shape is encountered in the fat of young animals especially 

 (see Plate XVIILj^. 1.); the second in that of adults (see 

 Jig. 2.) ; and the third in situations where the fat is sub- 

 jected to considerable pressure and on solidification after 



