554 



THE AMERICAN NATURALIST [Vol. LV 



I believe that the reason for the quicker growth in the 

 recovering animals lies, not in a faster growth rate in the 

 cycle, but in the shorter time between the maxima of the 

 two cycles. In other words, the final weight is reached 

 more quickly because the second cycle of growth com- 

 mences relatively earlier and is added to the first cycle. 

 Unfortunately, the weights of recovering animals were 

 not taken at sufficiently frequent intervals to afford data 

 upon the actual rates of growth in this class. 



If we assume that growth is the result of a catalyst 

 acting upon a substrate, it seems that we have a key to 

 the explanation of what is observed. The catalyst of the 

 first cycle was produced in the pre-natal stages. Al- 

 though there was no appropriate substrate available in 

 the starved animals, the catalyst did not disappear. 

 When an appropriate substrate was given, this catalyst 

 acted upon it, producing a cycle of growth essentially 

 equivalent to that showTi by animals fed on adequate 

 diets. This may mean that the catalyst persisted unim- 

 paired until it w^as destroyed in the course of the reaction. 

 The catalyst responsible for the second cycle likewise ap- 

 peared and induced the formation of fat. If the second 

 catalyst is in some way dependent upon a time factor for 

 its formation (or activation) it is plain that it should 

 show its activity relatively earlier in the case of animals 

 recovering from a long period of initial suppression, be- 

 cause of a quasi cumulative age effect. The effect of this 

 would be w^hat we have seen to happen, viz., a crowding 

 of the cycles nearer together. 



The writer is fully aware of the hazards encountered 

 in attempting to represent so complex a reaction as 

 growth by a simple formula. The phenomena of growth 

 appear, however, to be coordinated into a single self -con- 

 sistent process, in which many chemical and physical 

 factors are combined. The possibility of expressing 

 growth by a simple formula showing that an increase in 

 mass is definitely related with a function of time ought to 

 lead to considerations of a fundamental nature. 



