82 PROCEEDINGS: BOSTON SOCIETY NATURAL HISTORY. 
different ages, for, lie says, “the increase in weight depends on two 
factors, first upon the amount of body substance or, in other words, 
of growing material present at a given time ; second, upon the 
rapidity with which that amount increases itself. Hence for a given 
period the rate of growth may be expressed as the fraction of weight 
added during that period,” — in percentage increments. A curve 
of “percentage daily increments” for the frog is given in Fig. 8a. 
Fig. 8. Continuous line (a) represents the daily percentage increments, based on 
whole weight of tadpoles ; broken line (b) represents daily percentage increments based 
on dry weight of tadpoles. 
This curve is irregular ; it is certainly not rapidly ascending like Fig. 7. 
In studying his guinea pigs, Minot found that the curve of percentage 
daily increments was a rapidly descending one, (Fig. 6b), and he was 
led to suggest that there is a “ certain impulse given at the time of 
impregnation which gradually fades out, so that from the beginning 
of the new growth there occurs a diminution in the rate of growth.” 
The question arises, do the results obtained from embryo frogs 
confirm this hypothesis? 
In the first place our results indicate that the curve of percentage 
daily increments is of little significance for the frog and probably 
for organisms in general, on account of the fact that one assumption 
on which it rests is not justified. In the sentence quoted, Minot 
says, “ the increase in weight depends . . . upon the amount of body 
substance or, in other words, of growing material present at a given 
time.” An error seems to me to lie herein that not all the bodv 
