86 C. M. CHILD. 



however, showed a high percentage of complete reversals of 

 the gradient, death beginning nasally and proceeding apically, 

 the apical cell being the last to die. In some other hairs of this 

 group partial reversal of the hair gradient occurred, i. e., the 

 apical cell died first, and one or two cells below it in basipetal 

 order, while in more basal regions the progress of death was 

 acropetal, both from cell to cell and within the cells. In the 

 oldest hairs the hair gradient was usually basipetal, in the apical 

 third or half of the hair, i. e., for a length of three to five cells, 

 although the intracellular gradients were often acropetal, par- 

 ticularly in the more basal cells of this region. In the basal half 

 or two thirds of such hairs there was usually more or less reversal 

 of the hair gradient, the basal cell dying first, and one, two or even 

 three cells apical to it dying in acropetal order. The intracellular 

 gradients were very commonly acropetal in this region. In 

 short, by this exposure to high temperature the most susceptible 

 hairs were entirely killed, those of medium susceptibility showed 

 complete or nearly complete reversal and the oldest showed more 

 or less reversal in the basal regions. The susceptibility of all 

 living hairs and cells was of course much lower than that of cor- 

 responding hairs or cells in good condition tested at the same 

 temperature, and the susceptibility of the hairs of medium age 

 in which the gradient had been reversed was usually as low as, or 

 even lower than that of the oldest hairs. The experiment shows 

 a gradient in injury by the high temperature both in the single 

 hair and corresponding to age-differences in the tuft, the degree 

 of injury varying in general with the normal susceptibility of 

 different hairs and different levels. 



With short periods of exposure complete reversal was obtained 

 in the youngest hairs in many cases, partial basal reversal in 

 those of medium age and in some of the oldest hairs, but usually 

 only intracellular reversal in the more basal cells of the latter. 

 In this case the susceptibility of the youngest hairs was often 

 decreased below that of the oldest. 



Staining in neutral red so dilute as to give a barely perceptible 

 yellowish tinge to the water induced complete or nearly complete 

 reversal in some of the youngest hairs, but only more or less 

 reversal of intracellular gradients in the older. It was also 



