ix THE SKIN AND CUTANEOUS GLANDS 521 



are conflicting. Generally speaking, it may be said that the 

 thinner, less horny, and more vascular their skin, the better it is 

 adapted to absorption. Forlanini (1868) succeeded in poisoning 

 rabbits by simply treating the skin with aqueous solutions of 

 strychnine acidified with acetic acid. Other workers, however, 

 obtained negative results on rats and guinea-pigs (Wittich, Fubini 

 and Pierini). 



Signora Traube-Mengarini (1890) made a series of experiments 

 on the skin of dogs and man by painting the skin of the 

 abdomen (which is almost hairless) and the mammae with solutions 

 of borax carmine, of potassium ferrocyanide, and with medicinal 

 iodine for several days in succession. For human skin, a boy 

 was painted, once only, between the shoulders with tincture of 

 iodine. The animals were killed, and a bit of the boy's skin 

 removed, after 45 minutes, when the solutions applied to the 

 skin were sought for under the microscope the carmine being 

 fixed with sublimate, the ferrocyanide with ferric chloride (with 

 which it forms Berlin blue), and fresh sections being made of the 

 skin treated with iodine by the freezing microtome. 



The following results were obtained : (a) the carmine had 

 only stained the superficial layer of the epidermis ; (ft) the 

 potassium ferrocyanide had penetrated beyond the stratum 

 corneum into the superficial cells of the stratum granulosum ; 

 (c) the iodine, on the contrary, had penetrated all the layers of 

 the epidermis and corium, and .had been absorbed by the lymph. 



To interpret this penetration of iodine Signora Traube- 

 Mengarini concluded that it alters the skin chemically by forma- 

 tion of undefined compounds, particularly with the cutaneous fat. 

 It is known from previous experiments by Fleischer, Waller, and 

 Winternitz, that the absorption of various soluble substances, in 

 solutions of ether or chloroform, takes place more readily and 

 constantly in the skin of certain mammals than in that of man. 



Cataphoresis of soluble substances also occurs more easily in 

 these animals than in man. 



In the skin of frogs the conditions for absorption are still more 

 favourable, because there is no sebum. It is constantly moist, 

 and highly vascular. The fact observed by Eeid (1890) is interest- 

 ing to the effect that diffusion through living frog's skin takes 

 place more easily from without inwards, while in dead skin the 

 exchanges occur more readily in the opposite direction. This 

 proves that the absorption of which frog's skin is normally 

 capable is not a purely osmotic phenomenon, independent of the 

 vitality of the cells of which it is composed. 



According to Pesci and Andres (1901-2), both the living skin 

 of the frog and that of the higher vertebrates and of man behaves 

 as a semi-permeable membrane, which permits water to leave 

 or enter, according to the hyper- or hypo-tonicity of the solutions, 



