246 OF THE PRIMARY TISSUES OF THE HUMAN BODY. 



these form a minute plexus through the whole substance of the skin, which 

 becomes finer and closer as it approaches the surface, its branches at length coin- 

 ing to contain but one or two fibres each ; and from the most superficial portion 

 of the plexus, fibres pass up into the papillae, which there terminate in loops. 1 

 Thus we see that the Vascularity of the skin has purposes very different from 

 those which it answers in the Mucous membranes ; a large part of the blood 

 which this tissue receives, being destined to afford to the nerves of Touch the 

 means of their activity; and one chief office of the remainder being to supply 

 the material for the production of the protective Epidermis and its appendages. 

 It is only in the excretory action of the Sudoriparous glandulae, and in the slight 

 absorptive power which the Skin possesses, that we trace any functional relation 

 to the great Mucous membrane system. The Skin, in fact, ministers almost as 

 exclusively to the operations of Animal life, as do the Mucous Membranes to 

 that of Organic life. The nutrition of the various textures composing the Skin 

 may be considered to take place with an activity proportionate to their several 

 requirements; thus, whilst the various glandular organs, the hair-follicles, the 

 nervous papillae, and the muscular fibres, are continually drawing new elements 

 from the blood, it is probable that the fibrous tissues which constitute the essen- 

 tial basis of this texture are not more rapidly renewed than they are elsewhere 

 ( 220). The regeneration of the skin, after the loss of a portion of it by dis- 

 ease or injury, is effected with almost entire completeness. The new tissue is at 

 first more dense and less vascular than the old; but it soon gives such indications 

 of sensibility as make it evident that nerve-fibres must be very early formed, in 

 its substance; and the epidermis is normally developed from its surface. It has 

 been asserted that no tactile papillae are ever formed upon regenerated skin, and 

 that in the Negro the pigment-cells are not reproduced, so that the cicatrix 

 remains light. Neither of these statements, however, is correct; though it is 

 quite true that some time elapses before the pigment-cells of the Negro epider- 

 mis are formed again in their usual amount. It is not yet certain that the hair- 

 follicles and sudoriparous glands are formed in regenerated skin. 



240. The Epidermis usually forms a thin semi-transparent pellicle, in close 

 apposition with the surface of the Cutis, filling up the spaces between its papillae, 

 so as to obliterate its inequalities, and investing the whole with a stratum of 

 nearly uniform thickness (Figs. 37, 38); so that whilst its under side is pitted 

 for the reception of the cutaneous papillae, its outer or free surface is nearly 

 level. In some parts, however, the Epidermis is enormously increased in thick- 

 ness; such being particularly the case with those spots which are subjected to 

 continual pressure or friction, such as the palms of the hands and the soles of 

 the feet. Its substance consists of a series of flattened scale-like cells, which, 

 when first formed, are spheroidal, but which gradually dry up, their nuclei 

 also at last disappearing. These form several layers, of which the deeper can 

 be seen very distinctly to possess the cellular character, whilst the external layers 

 are scaly; and between these, all stages of transformation may be traced (Fig. 

 36) the outer layers being continually thrown off by desquamation, whilst new 

 ones are as constantly being formed below. The outer and inner portions of 

 the Epidermis, however, present a marked difference in character which is 

 made still more apparent by the use of reagents ; for whilst the former (Fig. 

 37, a) is a comparatively firm horny membrane, which is not affected either by 

 acetic acid, or by a moderately strong solution of potash, the latter is soft and 



1 The existence of this mode of termination of the Nerve-fibres, first admitted on the 

 Authority of Gerber, and confirmed by Purkinje and Krause, but looked for in vain by 

 other equally competent observers, has been lately established by Prof. Kolliker ("Mikro- 

 skopische Anatomic," band ii. pp. 24-31), who states that it may be traced with com- 

 parative ease, if the skin be first steeped in a weak solution of caustic soda. 



