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XCIV. Of the secretions.' It has been said, in too general a way, that 

 the organs receive from the blood conveyed to them by the arteries, the 

 materials of'the fluids which they separate from it. We have seen, that 

 the liver is a remarkable exception to this general rule; the same obser- 

 vation seems, likewise, applicable to the mammae ; they appear to receive 

 the elements of their milky secretion, from the lymphatics, which are so 

 very numerous in their structure *. 



One is, therefore, justified in saying, .that the elements of our fluids 

 may be furnished by vessels of every kind, to the organs in which such 

 fluids may be elaborated. The term secretion, whatever its etymology 

 may be, denotes that function by which an organ separates from the blood, 

 the materials of a substance which does not exist in that fluid, with its 

 characteristic qualities. By the term secretion, one should not, there- 

 fore, understand the mere separation of a fluid existing, before the action 

 of the organ by which it is preparedf. 



XCV. The difference between the secreted fluids, are evidently con- 

 nected with those of the organs employed in their formation. Thus, the 

 arterial exhalation which takes, place, throughout the whole extent of the 

 internal surfaces, maintains their contiguity, throws out an albuminous 

 serosity, which is merely the serum of the blood, slightly changed, by 

 the feeble action of a very simple organization. The analysis of the- 

 fluid of dropsy, which is merely the serosity constantly transuding from 

 the surface of the serous membranes, as the pleura and peritoneum, 

 shows, that it bears the strongest resemblance to the serum of the blood, 

 and that it differs from it only in the varying proportions of albumen and 

 of the different salts which it holds in solution. 



This first kind of secretion, this perspiratory transudation, would seem 

 to be a mere filtration, through the pores of the arteries, of a fluid already 

 formed in the blood. There is, however, besides, an inherent action in 

 the membranes whose surface it continually lubricates. If it were not for 

 this action, the serum would remain united to the other constituent parts 

 of the fluid, which is in too much motion, and at too high a temperature, 

 to allow of a spontaneous separation. The term exhalation, which is 

 applied to this secretion, gives an incorrect idea of it, for, exhalation, 

 which is a purely physical phenomenon, and requiring the presence of 

 air to dissolve the fluid that is exhaling, cannot take place from surfaces 

 that are in absolute contact, and between which there is no interval. The 

 character of this mode of secretion, is the absence of any intermediate 

 substance, between the vasa afferentia and the excretory ducts; the mi- 

 nute arteries and veins which enter into the structure of the membranes 

 being, at once, vasa afferentia and excretory ducts. The fluid secreted 

 by the serous membranes, though bearing a considerable analogy to the 

 serum of the blood, differs from it, however, by being animalizecl in a 

 greater degree. The most important function of these organs is, there- 

 fore, tt\at they concur in the common process of assimilation ; the office 

 which has long been assigned to them of fascilitating the motion of the 

 organs which they envelope, by lubricating their surface, will appear to 



* This opinion respecting 1 the source of the secretion of milk, is now relinquished by 

 M. Tlichciand. Copland. 



f Either the material <^ the fluid or the elements necessary to its constitution MUST 

 exist, before it can be separtued.- See Phil. Med. Jour. No. 5.Godman. 



