ix THE SKIN AND CUTANEOUS GLANDS 483 



derivative, belonging to the group of sclero- proteins, which is 

 known as keratin. The constitution of this is unknown ; it has 

 the same percentage composition as the proteins, but contains a 

 considerable amount of sulphur, partly in loose combination with 

 other elements, from which it separates on boiling in alkaline 

 solution. 



It is difficult to estimate the amount of horny substance 

 detached from the surface of the body in the form of epidermoid 

 scales. According to Funke. the loss of lamellae in the sweat 



O 



amounts to 6 grins, in 24 hours. Moleschott (1878), on the 

 strength of a fact observed on himself (viz. that a scrap of 

 epidermis sloughed off in a boil was regenerated in 34 days), 

 calculated ingeniously that an individual of average body-weight 

 must lose 14'35 grms. epidermis daily, containing 12'20 grms. 

 horny substance, and 2 - 10 grms. nitrogen. These figures are 

 exaggerated and incredible, and are based on improbable hypotheses, 

 particularly on the assumption that the epidermis of any cutaneous 

 area (from which it has been removed) is regenerated in the same 

 time in which it is renewed by successive desquamations over the 

 whole remainder of the normal cutaneous surface. 



Moleschott again (on the strength of data furnished him by 

 Berthold as to the growth of hairs in the beard, and those noted 

 by himself as to the growth of hair and nails, which are horny 

 tissues essentially analogous to the epidermis) computed the mean 

 daily product of these structures at 0'26 grms. i.e., far less than he 

 calculated for the epidermis alone. It is also remarkable that the 

 production of horny tissues is much diminished by age, that it is 

 greater in summer than in autumn, and is accelerated by frequent 

 removal. By leaving less time between one cutting of the hair 

 and the next, says Moleschott, the growth of the hair is accelerated. 

 To us, therefore, it appears logical to conclude that on removing 

 the skin from a cutaneous surface, e.g. by application of blisters, 

 it should be regenerated in a much shorter time than is required 

 for the complete renewal of the epidermis over the whole area of 

 the intact skin. 



The regeneration of the stratum corneum is effected by mitotic 

 division of the cells in the Malpighian layer. The karyokinetic 

 figures are seen only in the spiny cells, not merely in the deepest 

 stratum contiguous to the papillae of the corium, but in the less 

 profound strata as well. While these cells are multiplying, the 

 more superficial are changing into cells of the granular layer. It 

 is probable that the granules of these cells are those which form 

 the keratin, or become converted into it. The more superficial 

 cells of the stratum granulosum are simultaneously converted into 

 those of the stratum lucidum, and these lastly into the scales of 

 the stratum corneum. 



We shall consider the structure of the coriuin, and more 



