SOME CURRENT THEORIES 



449 



centage of the total weight or length at the beginning of each period 

 and may be called for convenience the percentage increment. The 

 percentage increments for different periods enable us to compare 

 the activity of the organic substance per unit of weight or length 

 in adding to the weight or length in each period, and we find that 

 in growth the percentage increments may decrease while the 

 absolute increments are still increasing. In other words, as growth 

 proceeds, the absolute increment in grams or miUimeters may 

 become greater, but the growth-activity of each unit of weight or 

 length already present is decreasing. 



TABLE XIII 



Weights of the Human Embryo and of the Child during 

 THE First Four Years after Birth 



An example from among the data used by Ostwald will make the 

 matter clear. Table XIII gives in the second column the weights 

 in grams of the human embryo at monthly intervals from the 

 second month to birth, as determined by Fehling, and of the child 

 after birth at intervals of three months during the first two years 

 and of one year each during the third and fourth years, as deter- 

 mined by Camerer. The third column of the table gives the absolute 



