8O C. M. CHILD. 



The most susceptible basal region is almost invariably dead, the 

 dead region usually including the two or three most basal cells 

 visible, and the gradient is usually completely reversed in the 

 more distal regions of the hair. Instead of being practically in- 

 stantaneous, as in the hair when in good condition, staining with 

 neutral red occurs very slowly, and a basipetal staining gradient 

 appears, i. e., the most distal cell stains most rapidly and the 

 rate decreases basipetally from cell to cell. The same basipetal 

 gradient appears in the course of death. 



In these hairs with reversed gradient the susceptibility of the 

 most distal region is not much altered ; this is the least susceptible 

 region, the last to die in the normal hair and the most susceptible 

 in the hair with reversed gradient, but its susceptibility is very 

 much the same in the two cases. The more basal the level, i. e., 

 the higher the original susceptibility, the greater the decrease in 

 susceptibility afterward, until in the more basal regions the cells 

 which were originally most susceptible of all are dead. 



The cells next to these dead basal cells show the structure of 

 dying cells as soon as they begin to stain, i. e., masses of aggre- 

 gated protoplasm which stain almost black are already present, 

 but include only a part of the protoplasm, and the remainder 

 stains diffusely in the usual way. When the death of such cells 

 is finally completed the remainder of the protoplasm is aggregated 

 into deeply staining masses in the usual way and the diffuse stain 

 disappears. In these cases the death-changes in a single cell 

 may extend over hours. It is a fact of considerable interest that 

 the cellular death-changes resulting from unfavorable conditions 

 in the laboratory or in nature are the same in appearance as those 

 occurring in neutral red and other killing agents. 



The very great change in susceptibility in some cells of the 

 hair after reversal of the gradient is indicated by the fact that 

 the cells of the more basal levels which die in one or two minutes 

 in neutral red when the hair is in good condition may survive 

 for twenty-four hours in neutral red after reversal. 



What happens in such reversal is apparently this. The hair 

 is very sensitive and under depressing environmental conditions 

 the basal, most susceptible region dies as it does in solutions of 

 killing agents in the laboratory. Next to this region are cells, 



