1 86 NUTRITION OF FARM ANIMALS 



for new material, as well as any surplus of new wood over that 

 immediately required, may be used indifferently as fuel for 

 warming the building. The case of the young animal, in which 

 protein is permanently set aside for growth, is a trifle more com- 

 plex but substantially the same considerations hold good. 



265. Functions of fats. In the case of the fats the energy- 

 bearing function is the predominant and obvious one. Fats 

 are a concentrated form of fuel, containing much more energy 

 per unit than any of the other nutrients. They supply much 

 energy in a small bulk and are, therefore, well adapted for the 

 storage of reserve energy in the body. 



The fats and closely related bodies (the lipoids), however, 

 are also important and apparently essential constituents of 

 protoplasm (75). The lipoids, therefore, have important 

 structural functions and an adequate supply of them in the 

 body is indispensable. From this point of view, some interest 

 attaches to the results obtained by a number of investigators 

 who claim to have shown that a certain minimum supply of 

 lipoids in the feed is essential, especially for growing animals. 

 The evidence, however, is negative evidence, i. e., experimental 

 animals failed to grow normally on a lipoid-free diet. In view 

 of the positive results obtained by Osborne and Mendel, 1 as well 

 as of the fact that both the simple fats and the phosphatids, at 

 least, can be synthesized freely in the organism, and taking into 

 consideration the extensive synthetic power of the body in 

 general, it is difficult to believe that the presence of lipoids in 

 the feed is indispensable, and more recent investigations have 

 afforded a different explanation of the observed facts (498). On 

 the other hand, it has been shown that the lecithins stimulate 

 growth and also that the fats appear, within certain limits, to 

 favor the production of milk fat. 



266, Functions of carbohydrates. The carbohydrates even 

 more distinctly than the fats serve chiefly as carriers of energy. 

 While containing less energy per unit than fats, they can, on 

 the other hand, be consumed in larger quantities and they 

 practically supply the greater part of the energy in the diet of 

 man and of farm animals. While the presence of carbohydrates 

 (dextrose) in the blood and lymph is essential, this appears to 

 be chiefly on account of their ready availability as fuel material. 



1 Jour. Biol. Chem., 12 (1912), 81. 



