﻿Bones of the Skeleton as an Index of Nutrition. 213 



cartilage cells will proliferate rapidly, and increase in the 

 length of bones will result ; and that in conditions of lower 

 nutrition only the osteoblasts will be able to proliferate, and 

 increase in the diameter of bones will result. Restated, 

 anabolic conditions determine macroplasia, or growth in 

 length; katabolic conditions, euryplasia, or growth in cir- 

 cumference. 



(c) Mechanism of Macroplasia and Euryplasia. — Macroplasia 

 is the result of a highly nutritive environment. The reason 

 for this appears to be that the fully specialised cartilage cell 

 is too absorptive, is too anabolic, to cope with a large supply 

 of food. Individuation and genesis, however, vary inversely ; 

 and, from the point of view of the cartilage cells themselves, 

 individuation is low, therefore, genesis is high. In result the 

 cartilage grows rapidly, but is rapidly replaced by bone ; the 

 limb bones increase in length, and, because of the high level 

 of chondro-genesis, the epiphyseal plates persist. On the 

 other hand, the individuation of the osteoblasts is successful, 

 that is, is relatively high, therefore their genetic energy is 

 reduced, and there is little tendency to unnecessary bone 

 formation. But the specialisation of cartilage cells is not 

 only unsatisfactory from the point of view of their resisting 

 the action of a too favourable environment, it is also unsatis- 

 factory in that it does not give a sufficiently wide margin to 

 permit them to prosper in an unfavourable environment ; 

 this is clearly shown by the calcification of the cartilages of 

 old men, and it explains the early disappearance of the 

 epiphyseal plates in poorly nourished individuals. Cartilage 

 cells are, therefore, to be looked upon as imperfectly 

 specialised. On the one hand, they are not economical cells ; 

 on the other hand, they perform no very active functions, and 

 are, therefore, unable to use up much of the potential energy 

 of their food supply ; in short, they are primitive organisms 

 which in the race of evolution have been left hopelessly 

 behind by the osteoblasts. Phylogeneiic as well as onto- 

 genetic evidence supports this conclusion. 



Further, in a lowly nutritive environment, euryplasia must 

 occur, for there is no rapid multiplication of cartilage re- 



