SECRETIONS OF THE SKIN. 103 
and form a compound gland on the rump, the oily matter 
of which is squeezed out by the bill, and spread over the 
feathers. What is termed the scené of an animal is proba- 
bly a volatile oil, secreted along with this unctuous matter 
from these sebaceous glands. 
2. Viscous Secretions.—In the animals with cold blood, se- 
cretions are produced, by the skin, of substances differing i 
quality from those of warm-blooded animals; but destined 
to serve the same purposes, namely, to protect the skin 
from the action of the surrounding element. ‘The fluid 
which is secreted, has never been examined with care. In 
some cases, it appears glairy and adhesive, as in the com- 
mon slug, resembling albumen ; or mucous and slippery, as 
in the common eel, approaching in its properties to gelatine. 
As this last animal, however, turns whitish when plunged 
in boiling water, the secretion likewise contains albumen. 
The pores from which this viscous matter is secreted, are 
frequently visible to the naked eye in the larger animals. 
They are connected, in fishes, with vessels which traverse the 
body under the skin, and contain the fluid; and they fre- 
quently appear on the surface in regular rows. 
Besides these two kinds of secretions poured forth by the 
skin, which may be named protecting secretions, there is a 
third, peculiar to quadrupeds, known under the name of 
Sweat. 
3. Sweat.—In ordinary cases, the sweat, as it escapes 
from the skin, is in a state of vapour, and invisible to the 
eye. The quantity, however, which flies off, is considera- 
ble; and has been estimated by Lavoisier and Secuin, 
to amount, in the human body, to 1 lb. 14 oz. in twenty- 
four hours. When collected on the interior surface of a 
glass vessel, it possesses the properties of pure water. When 
obtained from flannel worn on the skin for several days, it 
yielded to THENARD acetic acid, and common salt, toge- 
ther with an animal matter resembling gelatine, and traces 
