SEBACEOUS FLUIDS. 57 



example, that venoms may be applied with impunity to 

 certain mucous surfaces, while they produce poisonous effects 

 if introduced into the circulation. These agents are not 

 neutralized by the secretions of the parts, for they will 

 produce their characteristic effects upon the system when 

 removed from the mucous surfaces and introduced into the 

 circulation ; and it is reasonable to suppose that the mucous 

 membranes are capable of resisting their absorption. ' This 

 fact is proven by the following interesting experiment de- 

 tailed by Robin : 



Let an endosmometer be constructed, using a fresh 

 mucous membrane, on the surface of which the epithelium 

 and layer of mucus remain intact, and in the interior of 

 the apparatus, place a saccharine solution, and let the mem- 

 brane be exposed to a solution containing some venomous 

 fluid. The liquid will mount in the interior of the ap- 

 paratus, but the poison will not penetrate the membrane. 

 If the mucus and epithelium be now removed with the 

 finger-nail from, even a small portion of the membrane, the 

 poison will immediately pass through that part of the mem- 

 brane, and an animal may be killed with the fluid which 

 now penetrates into the interior of the endosmometer. 1 



These facts show that mucus is an important secretion. 

 It not only has a useful mechanical function, but it is in all 

 probability closely connected with some of the phenomena 

 of elective absorption which are so often observed, particu- 

 larly in the alimentary canal. 



Sebaceous Fluids. 



The general cutaneous surface is constantly lubricated 

 by a small quantity of a peculiar oily secretion, called 

 sebum, or sebaceous matter. This secretion is somewhat 

 modified in certain situations, and an analogous fluid is pro- 

 duced by glands of a peculiar structure opening into the 



' ROBIN, Lemons sur ks humeurs, Paris, 1867, p. 439. 



