THE RATE OF GROWTH 



97 



From the base line to the one marked "ten " is a pe- 

 riod of ten days, and you see that the guinea-pig in 

 adding to its weight ten per cent, for the nineteenth 

 time does it so slowly that it requires ten days and 

 more ; for the twenty-first time, nearly twenty ; for 



50 



40 



10% 



30 



20 



10 



-nTT 



4 5 6 7 8 9 I0 



I2 I3 I4 I5 16 17 18 19 20 21 22 232425 



FIG. 30. CURVE SHOWING THE LENGTH OF TIME REQUIRED TO MAKE EACH 

 SUCCESSIVE INCREASE OF 10 PER CENT. IN WEIGHT BY MALE GUINEA-PIGS. 



the twenty-second time, nearly forty days. At last 

 the number of observations becomes small, and the 

 curve grows irregular. Thus we demonstrate that as 

 the animal grows older it takes longer and longer to 

 add ten per cent, to its weight. In the other sex, as 

 the next slide shows, (Fig. 31), the same phenomena 

 can be clearly demonstrated ; here are the periods as 



