SEC11ETIONS 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 scent of an animal is proba- 

 bly a volatile oil, secreted along with this unctuous matter 

 from these sebaceous glands. 



2. Visaws Secretions. In the animals with cold blood, se- 

 cretions are produced, by the skin, of substances differing in 

 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 flics off, is considera- 

 ble ; and has been estimated by LAVOISIER and SKGUIN, 

 to amount, in the human body, to 1 Ib. 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 



