202 MANUAL OF HISTOLOGY. 



tripalmitin and tristearin, held in solution by another oily neutral fat, 

 triolein. The more of the solid fats there are contained in the latter, 

 the higher stands the liquefying point of the compound, and the easier 

 does it congeal after death into a hard suety mass. In keeping with 

 this there exist also differences between the various portions of the 

 body. The consistence of the fats of various groups of animals differs 

 likewise. In this respect the adipose tissue of the Carnivora and Pachy- 

 derms corresponds most nearly to that of the human being, whilst that 

 of the Ruminants and Rodentia appears to be much more solid. The 

 fatty tissue of Cetaceans and fishes is, on the other hand, of an oily 

 nature, a necessary condition on account of their living in water. Com- 

 bined with its fatty contents there exists, besides, a still unknown colour- 

 ing matter in the cell occasioning its yellowish tint. It is retained with 

 considerable tenacity by the residue which still occupies the envelope after 

 the greater part of the fat has left the latter, and communicates to it a 

 reddish yellow tinge, as already remarked ( 121). 



Now, as to the chemical constitution of the cells which contain these 

 fats, the following is all that is at present known on the subject. After 

 extraction of the oily contents by means of ether and hot alcohol, the 

 empty cell remains behind in a flaccid condition. Its membrane is not 

 affected by acetic acid, but treatment with the latter causes the exit of 

 globules of oil from it, an effect produced likewise by the action of sul- 

 phuric acid, and also by an elevation of temperature. Further, the 

 envelope offers a more or less determined resistance to the action of 

 caustic potash, and probably consists of a material allied to elastin. 



The physiological significance of adipose tissue corresponds partly to 

 that of the animal fats in general. It is well adapted, through the 

 contents of its cells (fluid at the normal temperature of the body), for 

 the distribution of pressure and for acting as padding. Further, it 

 is suitable for the filling up of certain interstices between portions of 

 the body which require a yielding material of the kind. Again, owing 

 to its bad conducting powers, it must restrain the giving out of heat, 

 and consequent cooling of the body. The fatty contents, besides, of 

 these cells, like other fats, undergo decomposition through the atmo- 

 spheric oxygen, especially when they leave the cavity of the cell and 

 return to the blood, the ultimate results of which process (after many 

 intermediate products have been formed) are the -generation of carbonic 

 acid and water, accompanied by the evolution of heat. 



The neutral fats of the tissue we are considering have their origin in 

 the oily constituents or matters adapted to fatty metamorphosis of our 

 food. This seems indicated by the rapid deposition of fats which takes 

 place under good nourishment. But an important physiological question 

 here arises. The fats of the alimentary matters enter the radicals of 

 the lacteals in a neutral form, are met with saponified in the blood, 

 and again as a neutral combination in the interior of the cell. What 

 now becomes of the glycerin which is set free in the animal juices by this 

 saponification, and whence comes the same organic body on subsequent 

 resolution of this soapy compound 1 In regard to these points we pos- 

 sess at present but few facts ( 18). That the protoplasm of the cell- 

 bodies plays an important part in the processes cannot, therefore, be 

 maintained without question. Just as little is known also about the. 

 series of changes produced in the elaboration of fats from albuminous 

 substances and hydro carbons. 



