146 SPECIAL HISTOLOGY. 



1-3 to 1-2 of a line, on the palm: and 



3-4ths to IJd of a line, on the sole of the foot, in which tAvo latter 

 localities the variations are greatest, independently of the circum- 

 stance, that in the furrows and at the joints the skin is thinner than 

 elsewhere. 



With regard to the proportionate thickness of the horny and mucous 

 layers I find, in some localities, that the latter is constantly thicker 

 than the former ; i. e., in all parts of the face, in the hairy scalp, in the 

 penis, the glans, the scrotum, the nipple, and the skin of the thorax 

 in man ; in the labia majora and minor a, on the back and neck. Here 

 the mucous layer is 3-6 times, or 2-3 times as thick as the horny layer, 

 according as its thickness is measured from the bases or from the points 

 of the papillae. ; in a few of the localities mentioned, however, the stra- 

 tum Malpighii is, in its thinnest parts, of the same thickness as the 

 epidermis, as in the glans. In the rest of the body both layers are 

 either equal in thickness, as in the external auditory passage, and here 

 and there upon the flexor side of the first two sections of the extremities, 

 or the horny layer is 2 to 5 times thicker than the mucous, and in the 

 thickest places even 10 to 12 times as thick. 



The absolute thickness of the stratum MalpigJiii varies (at the base 

 of the papilla?) between 0-007 and 0-16 of a line; where it is thicker 

 than the horny layer, it measures in the mean 0-04 of a line, where it 

 is thinner, 0*01 0-02 of a line. The horny layer by itself measures in 

 many places only 0-005 of a line, in others 1 line or more ; when its 

 thickness exceeds that of the stratum Malpigliii, it is generally about 

 0-1-04 of a line, when it is less, 0-01 of a line. 



45. Pliysical and Vital Properties. The epidermis is but little 

 elastic, flexible in the living condition and not easily frangible, softer 

 in the deeper than in the superficial layers. The cells contain, neither 

 in their membranes nor between them, any demonstrable pores (apart 

 from the sudoriparous ducts and hair-sacs, which, in a manner, have 

 their outermost portions hollowed out in the epidermis), and form a 

 very solid, hardly a permeable substance. Many experiments, especially 

 those of Krause, show, that the horny layer of the epidermis permits 

 no fluids, except those which act chemically upon it, as the mineral acids 

 and the caustic alkalies, to pass through it, either by pores or by 

 imbibition, or by endosmose and exosmose, while it readily takes up 

 gaseous matters, or easily vaporizable substances (alcohol, ether, acetic 

 acid, ammonia, solutions of chloride of iron in ether, of acetate of lead in 

 alcohol), and gives them off (cutaneous evaporation). This conclusion 

 is not invalidated by the undeniable passage of water, liquid substances, 

 ointments, and even solid matter (sulphur, cinnabar), through the unin- 



