664 PHYSIOLOGY OF THE DOMESTIC ANIMALS. 



Glycochol, through whose union with benzoic acid hippuric acid is 

 formed, is manufactured in the liver, the formation of hippuric acid 

 occurring probably both in the liver and kidneys. 



II. THE FATE OF THE FATTY CONSTITUENTS OF FOOD. 



It has been found that the fats contained in the food are largely 

 absorbed unchanged in the form of an emulsion, a small fraction only 

 being converted into fatty. soaps. Such absorption was, moreover, found 

 to occur mainly by means of the chyle-ducts and only partially through 

 the blood-vessels. It may, therefore, be stated that fats are absorbed 

 unchanged in the forms in which they enter the alimentary canal. The 

 attempt to trace the progress of the fats through the animal body will 

 be aided by the study of the changes which occur in the adipose tissue. 

 This, of all the tissues of the body, varies most rapidly and in widest 

 extremes. Within a short space of time, as in starvation, the adipose 

 tissue of the body may almost totally disappear ; while, on the other hand, 

 it may, under exceptional circumstances, accumulate with the greatest 

 rapidity. In describing the histology of adipose tissue it was stated that 

 the oil-globules appeared in the centre of the connective-tissue corpuscles 

 and at their expense, and the process was likened to the nutritive pre- 

 hension of food in a small mass of undifferentiated protoplasm, such as 

 the amoeba. 



The fat, we have seen, enters the blood in all important respects 

 unchanged, and the simplest explanation of the development of the adi- 

 pose tissue would be to suppose that the connective-tissue corpuscles, 

 by a process of vital appropriation, pick out the oil-globules from the 

 fluid in which they are bathed. Several difficulties, however, oppose 

 this simple theory. In the first place, it is well known that but a small 

 amount of fat deposited in adipose tissue can come directly from the fat 

 of the food : for, as is well known, the butter in cream is far in excess of 

 the fat contained in the food, and it has been shown that in a fattening 

 hog for every one hundred parts of fat in the food four hundred and 

 seventy-two parts are stored up as adipose tissue. Again, if animals are 

 fed on a meat diet and soaps they accumulate adipose tissue — a process 

 which is scarcely capable of being explained by the re-transformation of 

 the fats by taking up glycerin and giving up alkali. 



On the other hand, the fats of different animals differ in composition, 

 and if two animals of different species are fed with the same fat the 

 chemical composition of their adipose tissue will vary. Thus, for ex- 

 ample, if a dog be fed with meat, palmitin, stearin, and soap, the fat 

 of its adipose tissue will be found to contain olein fat as well as palmitin 

 and stearin. So it is, therefore, clear that the latter neutral fat must have 

 been manufactured by the organism. 



