352 EXCRETION BY THE SKIN AND KIDNEYS. 



in the long, white hairs of the head. It occupies one-fourth to one-third of 

 the diameter of the hair. The medulla can be traced, under favorable con- 

 ditions, from just above the bulb to near the pointed extremity of the hair. 

 It is composed of small, rounded, nucleated cells, which frequently contain 

 dark granules of pigmentary matter. Mixed with these cells are air-glob- 

 ules ; and frequently the cells are interrupted for a short distance and the 

 space is filled with air. The medulla likewise contains a glutinous fluid be- 

 tween the cells and surrounding the air-globules. 



Growth of the Hairs. Although not provided with blood and devoid 

 of sensibility, the hairs are connected with vascular parts and are nourished 

 by imbibition from the papillae. Each hair is first developed in a closed 

 sac, and at about the sixth month of intrauterine life, its pointed extremity 

 perforates the epidermis. These first-formed hairs are afterward shed, like 

 the milk-teeth, being pushed out by new hairs from below, which latter arise 

 from a second and a more deeply seated papilla. This shedding of the hairs 

 usually takes place between the second and the eighth month after birth. 



The difference in the color of the hair depends upon differences in the 

 quantity and the tint of the pigmentary matter ; and in old age the hair be- 

 comes white or gray from a blanching of the cortex and medulla. 



Sudden Blanching of the Hair. There are a few instances on record in 

 which sudden blanching of the hair has been observed and the causes of this 

 remarkable phenomenon fully investigated by competent observers ; and it 

 is almost unnecessary to say that a single, well authenticated case of this kind 

 demonstrates the possibility of its occurrence and is important in connection 

 with the reported instances which have not been subjected to proper investi- 

 gation. One of these cases has been reported by Landois. In this instance 

 the blanching of the hair occurred in a hospital in a single night, while the 

 patient, who had an acute attack of delirium tremens, was under the daily 

 observation of the visiting physician. 



The microscopical examinations by Landois and others leave no doubt as 

 to the cause of the white color of the hair in cases of sudden blanching; and 

 the fact of the occurrence of this phenomenon can no longer be called in 

 question. All are agreed that there is no diminution in the pigment, but 

 that the greater part of the medulla becomes filled with air, small globules 

 being also found in the cortical substance. The hair in these cases presents 

 a marked contrast with hair that has gradually become gray from old age, 

 when there is always a loss of pigment in the cortex and medulla. How the 

 air finds its way into the hair in sudden blanching, it is difficult to under- 

 stand ; and the views that have been expressed on this subject by different 

 authors are entirely theoretical. 



The fact that the hair may become white or gray in the course of a few 

 hours renders it probable that many of the cases reported upon unscientific 

 authority actually occurred ; and these have all been supposed to be con- 

 nected with intense grief or terror. The terror was very marked in the case 

 reported by Landois. In the great majority of recorded observations, the 

 sudden blanching of the hair has been apparently connected with intense 



