THE EVOLUTION OF DEATH 65 



increase of weight, does not show the rate of growth. The 

 real rate can be represented in the following manner with 

 approximate accuracy. From the weight which an animal 

 has on a given day and that which is found at the next weigh- 

 ing, I reckoned the average daily increase during the period 

 between the two weighings, and then changed these increases 

 into the per cent, value of the weight at the beginning of the 

 period. This method may be modified by calculating instead 

 of the daily, the monthly or yearly percentage increases. 



51117232935 ^5 60 75 90 105 120 135 150 165 180 195 210 days 

 FIG. 27. Curve of the daily percentage increase in weight of male guinea-pigs. 



The method is of course mathematically not exact, since the 

 weight is constantly changing. It suffices, however, for our 

 purposes. It is easy after one has calculated a series of per- 

 centage increments in weight to construct a curve. The 

 results obtained in this way I wish to lay before you. When 

 guinea-pigs are born, they suffer in consequence of the great 

 sudden disturbance of their conditions of living a temporary 

 inhibition of their development. They recover within two 

 or three days, and thereupon we observe that they may 

 increase their weight over 5 per cent, in one day, Fig. 27. 



