THE RATE OF GROWTH 95 



covered, and after that restoration they can add over 

 five per cent, to their weight in a single day. But by 

 the time they are 17 days old, as represented by this 

 line, they can add only four per cent, and by the time 

 they are 24 days old, less than two per cent; at 45 

 barely over one per cent; at 70 still over one per 

 cent; at 90 less; at 160 less; and towards the end 

 the curve continues dropping off, coming gradually 

 nearer and nearer to zero, to which it closely ap- 

 proximates at the age of 240 days. In about a year, 

 the guinea-pig attains nearly its full size. You notice 

 that this curve is somewhat irregular. Such is very 

 apt to be the result from statistics when the number 

 of observations is not very large. It means simply 

 that there was not a sufficiently large number of 

 animals measured to give an absolutely even and 

 regular set of averages. But the general course of 

 the curve is very instructive. In the earlier condition 

 of the young guinea-pig there is a rapid decline ; in 

 the later, a slow decline. The change from rapid to 

 slow decline is not sudden, but gradual, as you see 

 by the general character of this curve. 



In the next slide (Fig. 29) we can see immediately 

 that what I have asserted as true of the male is equally 

 true of the female, although the values which we have 

 differ slightly in the two sexes, and there are accidental 

 but not significant variations in this curve as in the 

 first Here also we observe at once an early period of 

 rapid decline in which the rate of growth is going 

 down and down a period of slight decline in which, 



