SECRETION. 287 



exist in the, blood, which are found in the secretions, as/- 

 brin, a fatty substance ; and some of the elements of the 

 bile. Some physiologists believe, that many of the secre- 

 tions do exist ready formed in the blood, but cannot be de- 

 tected by analysis. In proof of this, two ounces of bile have 

 been injected into the veins of a dog, but the blood of the 

 animal, which was analyzed a few moments after, exhibited 

 not a trace of bile. 



5. That secretion is a vital process and not a chemical 

 one, is evident from the fact^that it is so much under the 

 influence of the nervous system. For example, sorrow and 

 grief change the qualities of the bile : a fit of anger some- 

 times causes an excessive flow of it : it will also change the 

 nature of milk to such a degree, as to produce colic, vomit- 

 ing, and even convulsions in the infant that swallows i^ 

 Grief will also suspend the secretion of the gastric fluid, and 

 thus destroy the appetite ; while fear causes a cold sweat to 

 break out, all over the surface of the body. If the nerves go. 

 ing to any organ are divided, the function of secretion will 

 be suspended. It is doubtless owing in a great degree to the 

 changeful states of the nervous system, that the secretions 

 vary so much in quality as well as quantity at different pe- 

 riods. 



6. Though we are able to understand but little of the true 

 nature of secretion, we know that there are three kinds of se- 

 cretory organs, v'i2^, exlialent vessels ; follicles ; and glands.^) 



l.The exhalents are believed to be the termination of the arte- 

 ries, or capillaries^ and they are of two kinds, internal and 

 external ; the former terminating on all the surfaces within 

 the body ; and the latter on the outside. (Their use is to 

 soften and lubricate these parts) 



7. The fluid, which is thrown out by the serous mem- 

 brane which surrounds the brain, the lungs, and the contents 

 of the abdomen, as well as into the cavities of the joints, is 

 very similar to the water of the blood, and its use is, to keep 

 the parts in a moist state, and enable the organs to move ea- 



