122 PHYSIOLOGY AT THE FARM. 



tion naturally arises, if these fat corpuscles exert any special 

 function in the process of nutrition. The case stands thus: 

 the fat element is a universal constituent in mammals of 

 healthful chyle, the essential nutrient of the blood, and yet 

 this fat element is incapable of performing what must be re- 

 garded as the jnost important part in nutrition, namely, the 

 repair of the great living solids. It would certainly be satis- 

 factory if some special use of these never-failing fat-corpuscles 

 in the chyle of mammals were ascertained. It does not dim- 

 inish the difficulty, but essentially adds thereto, that it is a 

 fact recognised in physiology that the chyle in birds is trans- 

 parent. Is it that the active respiration of birds, extending 

 all over the bodily frame, burns away the fat which in other 

 animals gives whiteness to the chyle ? The progress of physi- 

 ology, it is to be hoped, will dissipate all such difficulties. 



In all considerations respecting animal nutrition, it is to be 

 borne in mind that the blood stands between the food and the 

 organism. The blood is the fountain of nutrition to all the 

 solids and fluids of the living frame. Nutrition is sometimes 

 spoken of as vascular and non-vascular, but there is in reality 

 no such distinction. Every solid of the body, and every fluid 

 except the blood itself, is beyond doubt extravascular. It has 

 been common to represent the epidermis and its appendages 

 as extravascular solids, in contradistinction to the skin, the 

 membranes, and the solids in general. But this obviously is 

 an oversight. The epidermis, as an outspread solid, is cor- 

 rectly described as non-vascular when compared with the out- 

 spread solid the skin, in the substance of which vessels every- 

 where abound. But as the skin is composed of a number of 

 minute organic parts, the aggregation of which constitutes the 

 entire skin, so the epidermis consists also of an aggregation of 

 a number of minute parts but the minute parts of which the 

 skin is made up are as much extravascular as the minute 



