26 



KNOWLEDGE. 



[February 1, 1899. 



large proportion of the red and yellow pigments may still 

 remain ; thus Sorhy found that some very black negro-hair 

 contained as much of the red constituent as an equal weight 

 of very red European hair. It would be interesting to pursue 

 this subject further, but the space at our disposal debars us 

 from being led into diverting speculations. It may, how- 

 ever, be noted that " blackness," as indicated either in hair 

 or skin, is a very unsatisfactory term. Sufficient pigment 

 may be present in a given weight of hair to impart to it a 



Kpidermie. 



V 





J^- 



Fig. 1. — Photomicrograpli of Section through Human Skin. 



colour which to us appears black, whilst another sample 

 of the same weight may yield three times the amount of 

 pigment and yet present no difference to the naked eye 

 from the first sample examined. It will thus be apparent 

 that by our ordinary methods of classification blackness 

 in the hair and skin may include a far greater range in the 

 amount of pigment present than at first appears probable. 



Without entering into a discussion of the probable 

 sources from which this pigment is derived, it may be 

 profitable to state that two opinions are held with regard 

 to its production. Some maintain that it is elaborated by 

 the cells of the deeper layer of the stratum mucosum, whilst 

 others hold that the pigment is brought to the cells from 

 other sources and is absorbed by them. The latter is more 

 probably the correct view, and is supported by evidence of 

 much weight. Thus, in the cells at the base of a hair 

 follicle, the pigment may often be seen blocking and filling 

 up the various inter-cellular channels ; it finally appears 

 within the cell and thus becomes intra-cellular. 



In recent times, since surgeons have adopted the process 

 of skin grafting to the healing of wounds and ulcers where 

 the skin has been extensively destroyed, some interesting 

 observations have been made. Thus, it has been noted 

 that when the skin of a white man is grafted on to a negro 

 the grafted patch assumes the normal tint of the individual, 

 and, rkr versa, when black skin is grafted on to white the 

 pigment disappears. Such evidence seems to support very 

 strongly the absorption as opposed to the elaboration 

 theory. One more point with regard to the growth and 

 structure of the skm may with advantage be referred to. 

 The generally accepted view with regard to the regeneration 

 of the superficial layers of the epidermis is, that the 

 deepest cells of the mucosum gradually advancing to the 

 suriace undergo a horny change and are finally shed on 

 the surface of the cuticle. So far such a view would meet 

 all the requirements of the case in the white races, but^ 



unfortunately, when we apply the same to the coloured 

 varieties we are met with a difficulty at once. As we have 

 seen, in the skin of the negro the deeper cells of the mucosum 

 are the cells which contain the most pigment, whilst the 

 superficial layers of the epidermis are free from colour. Now, 

 if, as has been suggested, the deeper cells advance to the 

 surface, it is only reasonable to suppose that they would 

 carry their pigment with them, and hence the superficial 

 layers would be as strongly coloured, if not more so, than 

 the deeper strata. We have already seen that the pigment 

 contained within these deeper cells is of a very stable 

 character, resisting the action of the strongest acids and 

 alkalies, and yet, if we adopt the accepted view with 

 regard to the regeneration of the superficial layers, we must 

 explain this disappearance of the pigment, which has not 

 yet been satisfactorily accounted for. But may it not be 

 that the accepted view with regard to the regeneration of 

 the superficial layers is at fault ? This is not the place to 

 enter mto a discussion of the matter, but possibly the 

 growth of the epidermis is analogous to the growth of 

 the cork cambium layer of plants. The mucosum cor- 

 responding to the green cells, the stratum corneum to the 

 corky layer of the cambium, and, if such be the case — and 

 there is much evidence in support of it — the deeper cells 

 would advance towards the surface of the cutis vera, that 

 is, they would grow inwards, whilst the horny cells would 

 grow towards the surface. 



Under these circumstances the active layers would be 

 those to which attention has been already directed, viz., 

 the stratum granulosum and the stratum Iwidum. Such 

 a view with regard to the regeneration of the epidermic 

 layers would explain many of the difficulties which we 

 encounter if we accept the current opinion. It would, as 

 will be evident, do away with the necessity for explaining 

 the mysterious disappearance of the pigment in the super- 

 ficial layers, and would afford a reasonable explanation of 



.ncnTn. 



lucidwiiu 



SImUtm 

 (irajitl/osuill. 



■■:i^^'j4 



V 



idV'XiU I'LTO. 



Fig. 2. — Pliutuiiacrograph of Section through Human Skiu more 

 highly magnified. 



how it happens that in old age a negro's hair becomes 

 white whilst his skin still retains its blackness, a detail to 

 which we may subsequently refer. 



Colour in man, then, may be said to depend on the 

 presence or absence of these pigments. In the fair races 

 there is probably a certain amount of the brown-red and 

 yellow pigment present, but in so small a quantity as not 

 to interfere with the transluceney of the layers ; in conse- 

 quence of this the reddish tint of the highly vascular cutk 



