THE CHEMICAL COMPOSITION OF FARM ANIMALS 31 



of the structural components consists principally of protein 

 material, growth may be defined as an increase in the pro- 

 tein tissue of the body. For the purposes of this book any 

 tissue, the dry substance of which is composed largely of 

 proteins, may be considered as protein tissue. It should be 

 note d that any increase in protein is always accompanied 

 by a large amount of water a nd a small amount of mineral 

 matter . Any considerable fa t production accompanying 

 the increase in protein tissue niayT)e regarded as incidental, 

 its amount depending upon the amount and nature of the 

 feed. 



Fattening consists in the deposition of fat in the cells 

 already present in the body, most largely in the cells of th e 

 i Qnseponnective tissu e. During the process the cytoplasm and 

 nucleus are pressed to one side and the cell wall may be 

 greatly distended. The^mainobject ot tattemn gls not th e 

 storage^f a large amount of fat for the nutritive value which 

 the fat contains, but to improve the flavor, tenderness, and 

 qua lity of the lean meat by the depositi on_ofJat between the 

 mnsnnlar jfih^rs- This mixture of fat and lean is much de- 

 sired by the butcher and consumer. It is known as 

 '' marbling." Figure 2 shows the desired marbling in a 

 porterhouse steak from a prime steer carcass. 



just_as__the norm al production of protein tissue during 

 growth is accompanie d by the production o f more or less 

 fatE^y tissue7 (^.g- tissue the dry substance of which is com- 

 posed largely of fat) so also a fattening animal, unless quite 

 mature, continues to grow~while l3eihg fattenedr Thus^ the 

 t m) proc ess es of growth and fatte m ng shaHej nto each other 

 an d no sharp distinction can be made between the m, as m 

 many cases both processes are taking place at the same time. 



