62 CELL-DIVISION AND GROWTH II. 2 



An inspection of the accompanying table and figure in which 

 Minot's results are reproduced will show at once that there is 

 in both sexes, almost from the moment of birth, a decline in the 

 growth-rate. The decline is not, however, uniform. The rate 

 falls rapidly between about the fifth day (when it is from 5 % to 

 6%) and the fiftieth, from the fiftieth day onwards more slowly, 

 becoming eventually very small, zero or even negative. The 

 younger the animal, therefore, the faster it grows ; the more 

 developed it is the more slowly it grows. The rate of growth 

 in faot varies inversely with the degree of differentiation. A 

 mammal, therefore, which is born in a less developed condition 

 than is the guinea-pig ought to grow at first more rapidly still. 

 The rabbit is such an animal, and Minot has been able to show 

 that on the fourth day after birth the young rabbit adds 17 % 

 to its weight. The curve also shows the same rapid decline in 

 the growth-rate as was observed in the guinea-pig, followed by 

 a period of gentle decrease. 



Accurate observations on the prenatal rate of growth of these 

 two mammals are lacking, but Hensen's few observations (quoted 

 by Preyer) on the weight of guinea-pig embryos show that the 

 daily percentage increase descends from 220% on the twenty-first 

 day to 116% on the twenty-ninth day, to 33% on the forty-third 

 day, and again to 6% on the sixty- fourth day, that is just after 

 birth, the moment at which Minof s observations begin. Again, 

 Minot has found, as a result of the investigation of the weight 



TABLE IV 



Showing the decrease in the rate of growth of the Human embryo before 

 birth. Percentage increments calculated from the figures given by 

 Hecker, Toldt, and Hennig. (From Preyer.) 



Average monthly percentage increments of 

 Month. Weight. Length. 



(Hecker.) (Toldt.) (Hennig.) 



1 



2 133-3 4330 



3 _ 100-0 110-0 



4 418-2 714 92-8 



5 398-2 66-7 69-8 



6 123-2 50-0 28-2 



7 92-2 16-7 14-2 



8 28-8 14-3 11-9 



9 25-6 12-5 6-3 

 10 11-1 43 



