GROWTH OF THE HAIRS. 339 



filled with air, and a few nuclei. The pigment may be of any color, from a light yellow 

 to an intense black, and it is this substance that gives to the hair the great variety in 

 color which is observed in different persons. In the lower part of the root the fibres 

 are much shorter, and at the bulb they become transformed, as it were, into the soft, 

 rounded cells found in this situation covering the papilla. 



The epidermis of the hair is excessively thin and is composed of flattened, quadran- 

 gular plates, overlying each other from below upward. These scales, or plates, are with- 

 out nuclei, and they exist in a single layer over the shaft of the hair and the upper part 

 of its root ; but, in the lower part of the root, the cells are thicker, softer, are frequent- 

 ly nucleated, and they exist in two layers. 



The medulla is found in the short, stiff hairs, and it is often beautifully distinct in 

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

 eter of the hair. The medulla can be traced, under favorable circumstances, from just 

 above the bulb to near the pointed extremity of the hair. It is composed of small, 

 rounded cells, from ^Vfr to y^ of an inch in diameter, nucleated, and frequently con- 

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

 globules ; and frequently the cells are interrupted for a short distance and the space is 

 occupied with air. The dark granules of the medullary cells are supposed by Kolliker 

 to be globules of air. The medulla likewise contains a glutinous fluid between the cells 

 and surrounding the air-globules. 



Growth of the Hairs. Although not provided with blood and deprived 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 its 

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

 like the milk-teeth, being pushed out, as it were, by new hairs from below, which arise 

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

 place from two to six months 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 becomes white or gray from 

 a blanching of the cortex and medulla. 



Sudden Blanching of the Hair. It is an interesting question, in connection with the 

 nutrition of the hair, to examine the instances so often quoted of sudden blanching of the 

 hair from violent emotions or other causes. Some physiologists are of the opinion that 

 the hair may become almost white in the course of a few hours, and this, indeed, is a 

 popular impression ; but others assume that such sudden changes never take place, 

 although it is certain that the hair frequently turns gray in the course of a few weeks. 

 In examining the literature of this subject, it is difficult to find, in the older works, well- 

 authenticated cases of these sudden changes, and most of those that have been quoted are 

 taken upon the loose authority of persons evidently not in the habit of making scientific 

 observations. Such instances, unsupported by analogous cases of a reliable character, 

 must necessarily be rejected as not fulfilling the rigid requirements demanded in scientific 

 inquiries, in which all possible sources of error should be carefully excluded. It is not 

 necessary, therefore, to quote the instances of sudden blanching of the hair recorded by 

 the ancient writers, or those well-known cases of later date, so often detailed in scien- 

 tific works, such as that of Marie Antoinette or Sir Thomas More; and it seems proper 

 to exclude, also, cases in which the blanching of the hair has been observed only by 

 friends or relatives ; for in most of them the statements with regard to time are conflict- 

 ing and unsatisfactory. 



Regarding the subject, however, from a purely scientific point of view, there are a 

 few instances of late date, 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 interesting in connection with the 



