56 



GROWTH 



As previously explained, when data plotted on arithlog paper 

 are distributed about a straight line, it may be concluded that 

 the percentage rate of growth is constant. Now the arithlog 

 charts representing data from thirteen days after conception 

 (that is nine days preceding birth) up to ninety-five days after 



Days 22 



Conception Age 



Figure 38. Growth data of the rat plotted on arithlog paper be- 

 ginning with birth (about 22 days after conception). There ap- 

 pears to be a drop in the percentage rate of growth ten days after 

 birth (about 5 per cent per day) and possibly another about one 

 month after birth (about 3 per cent per day). Puberty occurs 

 about 95 days after conception when the self-accelerating phase 

 of growth is changed to the self-inhibiting phase of growth. 



conception, shown in Figures 37 and 38, tell a somewhat differ- 

 ent story from the one conceived by Robertson. These two 

 charts say in effect that (1) up to puberty (about seventy days 

 after birth or ninety days after conception in the white rat) the 

 growth curve is made up of at least four segments, or, if one 

 prefers, "cycles" ; (2) the percentage rate of growth is con- 

 stant during the periods represented by the segments or cycles ; 



