PHASES IN THE LIFE OF THE INDIVIDUAL 665 



over one per cent, to their weight ; when ninety days old, less 

 than one per cent., and still less as they grow older, until when 

 about a year old they attain their full size. The curves in the 

 accompanying diagrams show the daily percentage increments 

 in weight in male and female guinea-pigs respectively, as ascer- 

 tained by Minot. It is seen that the curve for the females is 

 very similar to that for the males. Both show an early period 

 of rapid decline in which the rate of growth is quickly diminish- 

 ing, followed by a period of slight decline in which the curve is 

 still falling, but very much more gradually. (Figs. 142 and 143.) 



2Sfiii n a a isx AS 



zioday^ 



Fig. 143. — (From Minot's Problem of Age, Growth, and Death, 

 Gr. S. Putnam & Sons, and John Murray. ) 



Minot has also investigated the rate of growth in the rabbit 

 and in the chicken. The young rabbit, as is well known, is born 

 in a very immature state of development after a relatively 

 short gestation period. Correlated with this fact, it was found 

 that the male rabbit four days after birth is capable of adding 

 over seventeen per cent, to its weight in a single day. From 

 that time the percentage increment drops very rapidly, so that 

 at an age of twenty-three days the rabbit can only add a little 

 over six per cent. After about the fifty-fifth day the decline 

 in the growth rate, which has hitherto been rapid, becomes 

 more gradual. In the case of the chicken, Minot's results were 

 in a general way similar, but the rate of growth on the first day 

 it could be measured was a nine per cent, addition to the weight, 



