578 OP SECRETION AND EXCRETION. 



secretions, involve the liberation of many products of which the elements are 

 superfluous, and therefore injurious to the system if retained in it. Thus it has 

 been shown to be quite possible, that, in the production of Gluten (gelatin) from 

 Albumen, an equivalent of Choleic (tauro-cholic) acid may be generated ( 91, 

 VI.). The condition of Organic Chemistry, however, is not yet such as to allow 

 of anything being advanced with certainty under this head. From these various 

 sources, then, a large amount of effete matter is being continually received back 

 from the tissues into the current of the circulation, or is generated in the blood 

 by the changes to which it is itself subject; and it is the great object of the 

 Excretory apparatus to free that fluid from the products which would rapidly 

 accumulate in it, but for the provision which is thus made for their removal. 



621. Notwithstanding that, under ordinary circumstances, the several parts 

 of the Excretory apparatus are limited, each to its own special function, yet we 

 see that there are certain complementary relations between them, which make 

 the action of one to a certain extent vicarious with that of another. Such a 

 relation exists, for instance, between the lungs on one side, and the liver and 

 intestinal glandulse on the other ; for, the more active the respiration, the less 

 bile is secreted ; whilst, if the respiration be lowered in amount by inactivity of 

 body and a high external temperature, a larger proportion of unoxidized or im- 

 perfectly oxidized excrementitious matters accumulate in the blood, giving rise 

 to that augmented production both of the biliary and of the fecal excretions 

 which constitutes diarrhoea. 1 And thus, on the other hand, when the liver is 

 not adequately effecting the depuration of the blood from the constituents of bile, 

 an augmentation of the respiration by active exercise in a low temperature gives 

 most effectual relief. Still more obviously vicarious, however, are the kidneys 

 and the skin ; for here we find that not only do the kidneys allow the transu- 

 dation of whatever superfluous water may remain in the circulating current, 

 after a sufficient amount has been exhaled from the skin to keep .down the tem- 

 perature of the body to its normal standard, but the skin actually assists in the 

 elimination of one of those products of the metamorphosis of the azotized tissues, 

 the removal of which has been until recently considered as the special function 

 of the kidney. Consequently, whenever the due action of the skin as an ex- 

 creting organ is interfered with, it is the kidney especially that will be called 

 on to take its place ; whilst, on the other hand, if it be thought necessary to 

 relieve the kidney, this may be most effectually done by stimulating the skin to 

 increased excretory activity. 



622. This vicariousness of function among the Excretory organs presents 

 itself far more remarkably, however, in certain states of disease ; in which a 

 complete "metastasis of secretion" exhibits itself. The capability of one organ 

 thus to take upon itself the special actions of another, seems to have reference 

 to the community of function which exists in the secreting surface among the 

 lower animals, in which there is none of that " specialization" or setting apart 

 for particular offices, which we see in the higher ; for it seems to be a general 

 law in Physiology, that, even where the different functions are most highly 

 specialized, the general structure retains, more or less, the primitive community 

 of action which characterized it in the lowest grade of development. 3 It is in 

 regard to the Urinary excretion, that the evidence on this point is most com- 

 plete ; for it seems to be established by a great mass of observations, that urine, 

 or a fluid presenting its essential characters, may pass off by the mucous mem- 

 brane of the intestinal canal, by the salivary, lachrymal, and mammary glands, 



1 Such is probably the occasion of the "bilious attacks" and "autumnal cholera" so 

 prevalent at the close of the summer ; the subjects of these being most commonly persons 

 who have not reduced their consumption of food during the warm season, in accordance 

 with the diminished demand for the production of heat within the body. 



2 See "Princ. of Phys., Gen. and Comp.," \\ 351, 605, Am. Ed. 



