SECKETION AND ABSORPTION BY THE SKIN. 

 By E. WAYMOUTH EEID. 



CONTENTS : Chemical Nature of Skin Secretions, p. 669 The Secretion of Sweat, 

 p. 676 Electro-Motive Phenomena in Skin Glands, p. 681 Absorption by the 

 Skin of Man, p. 685 -Of lower Mammals, p. 688 Of the Frog, p. 690. 



SKIN SECKETIONS. 



Comparative. The secretions of the skin in vertebrates fall readily 

 into two main classes (a) Those in which a watery solution is elabo- 

 rated by the gland-cells, and (b) those in which products of metamor- 

 phosis or degeneration of the gland-cells themselves form the secretion. 



As types of the former class may be instanced the sweat of 

 mammals, and the slime of fish and many amphibians ; of the latter, 

 the secretion of the various modifications of sebaceous glands in 

 mammals ; of the uropygial gland of many birds ; and the fibre secre- 

 tions of the skins of certain fish (Myxine, Anguilla, etc.). 



Such secretions are put to a variety of uses in the vertebrate series. 

 Of the first class, the sweat of the mammal is at once an excretion and 

 a means of regulating body temperature by evaporation, while the 

 slime of the frog or fish is protective in function. Of the second class, 

 the gr easiness of the sebum of the mammal, or secretion of the tail 

 gland of the bird, protects skin, hair, or plumage from imbibition of 

 water ; the secretion of the Meibomian glands of the eyelids prevents 

 overflow of tears ; the viscosity of the ear wax interferes with the entrance 

 of foreign bodies into the auditory canal ; while, in special cases, volatile 

 substances of good or evil odour, contained in the secretion, may serve 

 the purposes of sexual attraction or protection from enemies. 



In hairy mammals, it is only in certain cases, or on certain parts of the body, 

 that sweating is observed. Rabbits, rats, and mice are not known to sweat at 

 all, the dog sweats but little, the cat only on the hairless pads of the feet ; 

 while on the other hand the horse sweats profusely on all parts. The snouts 

 of pigs and oxen contain glands similar to sweat-glands, the secretion of which 

 keeps the part moist. 



Instances of glands used for purposes of sexual attraction are the glands of 

 the suborbital pit of many ruminants and some hogs, the cheek gland of the 

 elephant, the pectoral glands of certain tropical bats, the flank glands of shrews, 

 the sacral gland of the peccary, the groin glands of antelopes, the preputial glands 

 of the beaver and musk-deer, the anal glands of the hare, marsupials, armadillos, 

 two-toed sloth, otter, hyaenas, and civets, and the glands at the base of the tail 

 of shrews and the fox. The anal glands of the skunk are used for protection. 



The hoof gland of most bisulcate ungulates, opening in the cleft between 

 the two divisions of the hoof, is probably of use in protecting the horny 



