VICARIOUS SECRETION. 757 



Whatever the influence of the nervous system upon secretion, it 

 may be centric, or peripheral, and either simple or reflex, according 

 to the part in which the stimulus originates, or to which it is applied. 

 Tears are shed, and saliva flows, under the centric stimulation of 

 painful or joyous emotions, and on the occurrence of ideas relating to 

 food; whilst the same secretive acts are performed under reflex action, 

 from neuralgia of the fifth cerebral nerve, or from local irritation of 

 the conjunctiva or of the mouth. 



When, either from disease of the glands, or from an over-accumu- 

 lation, in the blood, of the materials to be excreted, these are no 

 longer eliminated through the usual organs, they are sometimes vica- 

 riously eliminated through some other gland or membrane. Thus, 

 urea has been found in almost every secretion and excretion of the 

 body, in the gastric and intestinal discharges, in the lachrymal and 

 salivary fluids, in' the nasal mucus, in the synovial and serous fluids, 

 the perspiration, and even in the milk. The pigment of the bile, which 

 is probably more of an excretory than a secretory product, occasion- 

 ally appears in the renal excretion and in other fluids of the body. 

 These are instances of real vicarious excretion, but in regard to the 

 secretions proper, no such metastasis, or transference, of secreting 

 power has been observed, no authentic example of milk secreted by 

 the liver or kidneys, or of saliva formed by the mammary gland, hav- 

 ing yet been met with. The presence of the coloring matter of the 

 bile in various true secretions, as in the pancreatic juice, the milk, the 

 mucus of the bronchial glands and membrane, and even in the serous 

 and synovial fluids, is perhaps only an apparent example of vicarious 

 secretion ; for, in these cases, the coloring matter of the bile is prob- 

 ably reabsorbed into the blood, and then is simply exuded into all 

 parts of the body with the common nutrient plasma, and so tinges the 

 various solid tissues, organs, glands, arid secretions. There is, more- 

 over, no evidence that, even in these cases, the more abundant and 

 truly secretory products of the hepatic cell action, viz., the soda salts 

 of the biliary acids, accompany the bile pigment in its passage through 

 the body, or into the secretions of other glands. The biliary pigment 

 probably represents an excretory part of the bile, and, if not pre- 

 formed in the blood, is easily dissolved and taken up by it, and thus it 

 may obey a true metastasis like other excretory substances. It cer- 

 tainly appears very readily in the urine, and also sometimes in the 

 perspiration. 



Certain excretions are complementary to each other, as, for exam- 

 ple, those of the lungs and the liver. The more abundant the excre- 

 tion of carbon in its perfectly oxidized form of carbonic acid gas from 

 the lungs, the smaller is the amount of carbonaceous compounds ex- 

 creted in the bile ; whilst, on the other hand, when the respiratory 

 changes are diminished through heat of climate, or defective exercise, 

 the biliary products are increased. The excretions of the skin and 

 the kidneys, are also, to a certain extent, complementary to each 

 other, not only as regards their aqueous constituents, in respect of 

 which, each is, moreover, supplemented by the lungs, which give off 

 more or less vapor according to the relative degree of the moisture of 



