704 the; physiology of reproduction 





in Mammals represents the course of the autocatalytic synthesis of 

 the nuclear substance, that the third cycle represents the period 

 during which cytoplasmic material is built up, while the second 

 growth cycle is intermediate, representing a time when both 



synthetic processes go on con- 

 temporaneously. 



Growth of the Body befoee 



BlETH 



Minot^ ■ has recorded the 

 results of weighing embryo 

 rabbits at different stages of 

 development with a view to 

 determining their rate of growth. 

 The results showed that in the 

 period from the ninth to the 

 fifteenth day the young rabbit 

 adds on an average 7(i4 per 

 cent, to its weight daily, and 

 that in the period from the 

 fifteenth to the twentieth day, 

 the average daily addition is 

 only 212 per cent. It may be ' 

 assumed, therefore, that in 

 younger embryos (before the 

 ninth day) there is an increase 

 of over a thousand per day. 

 Minot estimates that over 

 ninety-eight per cent, of the 

 original power of growth of the 

 rabbit or the chick has been lost 

 at the time of birth or hatching, 

 and that a similar fact is equally 

 true of man. " We start out at 

 birth certainly with less than 

 two per cent, of the original 

 growth power with which we 

 were endowed. Over ninety- 

 eight per cent, of the loss is accomplished before birth — less than 

 two per cent, after birth," The accompanying diagram represents 

 roughly, the rate of growth in man before birth. The time intervals 

 correspond to the ten lunar months of gestation. The rate of 

 increase in the first three months is not indicated, since there are 



^ Minot, loe. cit. 



Fig. 174.— (rrom C. S. Minot's PTO6Z«m 

 of Age, Growth, and Death, G. S. Put- 

 nam & Sons, and John Murray.) 



