OLEAGINOUS COMPOUNDS. b9 



which attends the first solution of Chondrin cannot, however, be thus explained ; 

 and must be imputed to some peculiarity in the molecular aggregation of the 

 substance, which does not manifest itself in a fibrous arrangement. It is inte- 

 resting to remark that, of all the gelatigenous tissues, there is not one which can 

 be said to have other than mechanical functions, such as that of binding parts 

 together, resisting tension, or antagonizing pressure. On the other hand, all 

 the proper vital functions of the body are performed by tissues whose composi- 

 tion is albuminous. 



3. Oleaginous Compounds. 



36. We now arrive at the non-azotized division of the organic compounds 

 entering into the composition of the animal fabric; and the first group to be 

 noticed, as connecting the histogenetic substances with the mere combustive 

 materials, is that of the Oleaginous or Fatty matters. These are pre-eminently 

 remarkable for the small amount of oxygen which enters into their composition, 

 and for containing carbon and hydrogen in nearly equivalent proportions; they 

 are soluble in ether and hot alcohol ; but they are insoluble in cold alcohol and 

 in water. Fatty substances are ranked as saponifiable or non-saponifiable, 

 according as they are or are not decomposed by strong bases, such as alkalies 

 or the oxide of lead. When this decomposition takes place, the fatty matter is 

 separated into two constituents ; an acid, which unites with the stronger base to 

 form a soap or a plaster; and a weak base, which is set free. How far this acid 

 and base have a separate existence previously to the act of saponification, or are 

 formed in the process itself, cannot at present be positively stated. It is a re- 

 markable fact, however, that the separation of the fatty acids from their base 

 may be effected also by the agency of putrescent albuminous matters ; and this 

 has been shown by Lehmann to occur during the fermentation of milk. 



37. The fatty substances which present themselves most largely in the Human 

 body, are Margarin and Olein ; the former of these being solid when separate, 

 but being dissolved in the latter (which retains its fluidity when cooled down 

 below Fahr.) at the ordinary temperature of the body. In the fat of most 

 other animals, the Margarin is replaced by Stearin; and these two substances, 

 as will be presently shown, have very close chemical relations. Margarin 

 exists in small quantity, along with stearin, in most animal fats; and it is the 

 principal solid constituent of the vegetable fats, with which, therefore, Human 

 fat more closely corresponds than does that of most other animals. It is a white, 

 solid, spermaceti-like substance, which melts at 118, and which crystallizes 

 from its solution in hot alcohol as a flocculent white powder, that is found by 

 the microscope to consist of very delicate and often curved needles, often so 

 grouped as to radiate from a central nucleus, an appearance not unfrequently 

 seen within the cells of Adipose tissue. Stearin is also a spermaceti-like sub- 

 stance ; but its melting-point is higher, namely, 144 ; and it separates on 

 cooling from its solution in hot alcohol (which takes up less of it than of mar- 

 garin) in snow-white glistening scales, which are either rhomboidal tablets, or 

 short rhombic prisms. Olein exists in small quantity in the solid fats, but con- 

 stitutes the principal part of the fixed oils; and the tendency of these to solidi- 

 fication by cold depends upon the amount of stearin or margarin which they 

 may contain. When separated from these, it is a simple colorless oil, which 

 has a peculiar tendency to become rancid on exposure to the air. The follow- 

 ing results of the ultimate analyses of the fat of different animals, by Chevreul, 

 will show the close correspondence in their composition ; whilst it also makes 

 apparent the very large proportion of Carbon which they all contain. 



