DEVELOPMENT 259 



produce a pound of gain, but on the other hand the gain in 

 live weight was accomplished by feeding only five and six 

 one-hundredths pounds of grain and two and four-tenths 

 pounds of hay for each pound of gain. The steer that 

 had been fed generously for the first twelve months of 

 its life gained only 500 pounds during the period in 

 which the stunted one had gained 842 pounds. In the 

 production of the 500 pounds the full-fed steer had con- 

 sumed nine and eight-tenths pounds of grain and four 

 and two-tenths pounds of hay for each pound of gain in 

 live weight. Over forty per cent less feed was required by 

 the stunted animal for each pound of increase in live 

 weight. Not only did the stunted animal not lose 

 its capacity to grow, but in certain respects its growth 

 processes were accelerated during the period covered 

 by this experiment as a result of its difficult struggle 

 for existence during the first twelve months of its 

 life. 



246. Growth and the cell. Increase in the size of 

 animals which follows growth is due to a multiplication 

 of cells and not to an increase in their size. The size 

 of cells varies between rather narrow limits. The larger 

 size of some animals is not due to larger cells in their 

 organization but to a larger number of cells. It is also 

 true that the cells in any individual animal vary but 

 little in size. The increase in size of any part of an animal 

 is due, therefore, to an increase in the number of cells 

 and not to -an expansion of cells already formed. It is 

 true, of course, that certain minor exceptions to this rule 

 are to be observed. The nerve cells vary in size with the 

 size of the animal. The nerve cells of an ox are much 

 larger than those of the pig. The frog has very large 

 cells, while the starfish is composed of small cells. But 



