﻿Bones of the Skeleton as cm Index of Nutrition. 211 



the cells of the osteogenetic layer of the primitive 

 periosteum rapidly multiply and topographically replace 

 their predecessors. 



It is convenient here to digress for a moment to consider 

 what these phenomena mean from the point of view of 

 the cartilage cells. 



In some of the lower animals, the skeleton remains 

 cartilaginous throughout life. In other words, the supply 

 of nutrition to the cells is balanced so that a specialised 

 cartilage cell just receives sufficient nutriment to enable 

 it to perform its function of keeping the cartilaginous 

 matrix refreshed and healthy, whereas, in the higher 

 animals, as in man, the supply of nutrition is more than 

 the cells can profitably use. Overfed, they increase in 

 bulk, the increase of surface is necessarily disproportionate 

 to that of content, and so there is less opportunity for 

 nutrition, respiration, and excretion. Waste gains up, over- 

 takes, balances, exceeds repair, and brings about dissolution 

 and death.^ 



To resume ; the cells from the osteogenetic layer penetrate 

 right to the centre of, and there absorb the cartilage, eating 

 out a space, the primitive marrow cavity, which they occupy, 

 and in which they proliferate to form a tissue, the primitive 

 marrow. From this there arise the cells which are known 

 in histology as the osteoblasts and the osteoclasts. Around 

 the primitive marrow cavity the surfeit and the death of 

 the cartilage cells continue, but before the cells attain to 

 their fatal specialisation the safety of the race has been 

 temporarily, at least, provided for by genesis, one of the 

 daughter cells apparently always escaping to the side of 

 less pressure, that is, to the side where the cells are still 

 smaller. The result of this is seen histologically in the 

 almost columnar arrangement of the cells. Between the 

 columns the matrix, unrefreshed by its guardian cells, which 

 have died or are dying, undergoes calcification. As a 

 result, the edge of the dying cartilage is serrated by the 

 advancing swarm of osteoblasts; the dead bodies of the 



1 V. S. 



