SECRETION AND ABSORPTION BY THE SKIN. 
By E. "Waymouth Reid. 
Contexts : — 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 Secretions. 
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, Awjuilla, 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 greasiness 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, ripening in the cleft between 
the two divisions of the hoof, is probably of use in protecting the horny 
