GROWTH AND SENESCENCE 



55 



all possible, for the infantile and the juvenile cycles. This natu- 

 rally leaves room for differences of opinion regarding the 

 reality of the Robertsonian cycles. 



To throw further light on this question, we have plotted the 

 weights of the rats represented in Figure 36 on arithlog paper. 



Daus 13 15 f7 19 



23 25 2? 29 3t 33 



Acje 



Figure 37. Growth data of the rat plotted on arithlog paper. 

 The data points are distributed about a straight line from 13 

 days after conception until birth. The slope of the line indi- 

 cates that growth during this period takes place at 53 per cent 

 per day. At birth, there is a sudden break, a "metamorphosis," 

 and a drop to a lower but (approximately) constant percentage 

 rate (of about 12 per cent per day). 



