OF THE SKIN. L39 



The absolute thickness of the stratum Malpighii varies (at 

 the base of the papillce) between 0007 and 016'"; where it is 

 thicker than the horny layer, it measures in the mean 00 1"; 

 where it is thinner, 001 — 002"'. The horny layer by itself 

 measures in many places only 0005"', in others 1'" or more; 

 when its thickness exceeds that of the stratum Malpighii, it is 

 generally about 0-1 — 0-4"', when it is less, O'Ol"'. 



§ 45. 



Physical 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 con- 

 tain, neither in their membranes nor between them, any demon- 

 strable pores (apart from the sudoriparous ducts and hair-sacs, 

 which, in a manner, have their outermost portion hollowed 

 out in the epidermis), and form a very solid, hardly 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 (cuta- 

 neous evaporation). This conclusion is not invalidated by the 

 undeniable passage of water, liquid substances, ointments, and 

 even solid matters (sulphur, cinnabar), through the uninjured 

 epidermis, since in these cases a mechanical intrusion of the 

 substances, in and through the sudoriparous ducts and hair-sacs, 

 or their penetration into the sweat-ducts, and mingling with 

 the sweat, explains their absorption. The mucous layer, at any 

 rate, is easily penetrated by liquids, as is sufficiently shown by 

 pathological anatomy (exudations which penetrate the mucous 

 and raise up the horny layer into a vesicle, the ready occurrence 

 of absorption after the separation of the horny and the super- 

 ficial portion of the mucous layer, by the action of vesicants.) 



In their chemical relations, it is indeed well known how the 

 cells and plates of the epidermis behave with regard to certain 

 reagents, but there exists, at present, no perfectly satisfactory 



