GROWTH 



267 



of their growth: either they all multiply at the same 

 moment, or their reacting molecules follow definite 

 chemical rules, and the order of multiplication is governed 

 by these laws. The latter case is more probable, and 

 the theory is supported by the facts. 



It may be assumed that the molecules in a number of 

 uniform cells react as if all cell contents were one con- 

 tinuous fluid. This assumption seems permissible at 

 least for the molecules of the genes because genes do not 

 react with one another. In this case, the doubling of 

 any one certain type of gene molecule must follow the 

 mass law, and as there is only one such molecule for each 

 cell, it can be computed in what order this gene in the 

 different cells will double. It can also be computed in 

 which order any of the other genes, or each molecule of 

 each gene, will double. From this, the probability that all 

 genes in a cell have doubled, can be ascertained. This 

 probability gives us the variation of the rate of cell 

 division. 



The calculation has been carried out for various 

 numbers of genes (or molecules) in the chromosomes. 



Figure 26 represents one such series. It shows that 

 uniform cells under uniform environment will not all 

 divide at the same rate, but that for chemical reasons, 

 i.e., on account of the mass law, they must display con- 



