SECT. 2] AND WEIGHT 453 



where D is the dimension in question, L the total body-length, and 

 a and b constants. The constant ^ is a measure of the amount of 

 growth that has gone on prior to the period in question, and, as it is 

 negative for the limbs but positive for all head and neck measure- 

 ments, the conclusion is that while the latter have been growing 

 extremely rapidly before the period began the former have not. This 

 is as would be expected. The same conclusion emerges from the data 

 of Corrado on the weights of head, trunk and extremities as analysed 

 by Scammon. 



Many organs have been examined by the investigators of this 

 school. The cerebellum, for instance, was found by Scammon & 

 Dunn to increase in absolute volume and weight first slowly and 

 then more rapidly during the foetal period; thus, its percentage 

 growth-rate rose for the first six months of pregnancy, only to fall 

 sharply afterwards. The pancreas, studied by Scammon, grows at 

 a rate very like that of the whole embryo, but the relative weight 

 of the organ with respect to total body-weight undergoes a 

 reduction from 0-3 per cent, at the 4th month to o-i per cent, at 

 birth. The uterus, on the other hand, passes through two definite 

 phases in pre-natal life. Until 7 months the organ shows a lineal 

 increase with respect to body-length which is comparable to that 

 of most lineal body-dimensions, but after 7 months it grows much 

 more rapidly. In early post-natal life, however, the organ goes 

 through an involution stage which has long been known, actually 

 decreasing in size by hypoplasia and hypotrophy until it reaches 

 the level it would have attained had the early foetal growth-rate 

 been continued. "This suggests", says Scammon, '^that the growth 

 of the uterus in the latter foetal months consists of a substratum of 

 typical foetal growth plus a secondary increment due to an extra 

 stimulus furnished by a hormone of placental or possibly ovarian 

 origin." Here is an excellent illustration of how an organ can act 

 as an index registering obscure physico-chemical changes in the 

 internal environment of the embryo. The other organ which 

 undergoes a reduction in size following birth in man is the 

 suprarenal gland, and it also has been investigated by Scammon. 

 But, unlike the uterus, its growth when observed in the foetal 

 period shows no increased intensity towards the time of birth, so 

 that the involution which occurs afterwards by degeneration of 

 the two inner cortical layers decreases its size far below what it 



