190 VICARIOUS SECRETION. 



precise, the less and less does it appear probable that the secreted matter 

 is in any way engendered by the gland itself. 



Since, with the exception of the lungs, which excrete carbonic acid and 



. vapor of water, all the great glands remove the material they 



glandular are concerned with in a state of liquid solution, it follows of 



necessity that the blood of the artery supplying the gland, and 



that removed by the vein from the gland, differ in two respects : 1st. In 



the peculiar material constituting the solid secreted ; and, 2d. In the 



quantity of water. From the latter cause it must follow that the venous 



blood will have a greater spissitude than the arterial. 



This elementary or typical form of a gland is but very little departed 

 from in those cases in which the sac is elongated into a tube ; and even 

 where this has been extended to an exaggerated degree, the essential 

 principle of action still remains the same. 



From the constancy of aspect which glands present, we might be led 

 Influence of at first to suppose that their peculiarities of construction de- 

 by'viSous a<> termme their physiological action, that the liver secretes bile, 

 tion. and the kidney urine, because they have the special organ- 



ization which is needful for such purposes. Such a supposition, how- 

 ever, has to be received with much limitation, as is proved by number- 

 less cases of vicarious action. Thus, in morbid difficulties of the liver, 

 the skin will discharge its duty for it in the elimination of the bile ; and 

 in derangements of the kidneys, the mammary gland, the mucous mem- 

 brane of the nose, or even the stomach, will discharge urine. Construct- 

 ive arrangements have therefore for their object the facilitating of a secre- 

 tion, but they do not produce it. Thus the liver is far better fitted for 

 separating bile, or the kidney urine, than is the skin for each of these re- 

 spectively ; but if they become incapacitated, the skin is able to act vica- 

 riously for them. 



Though such vicarious action has been denied by some physiologists 

 Connection of as being totally incompatible with anatomical indications, a 

 tioiuinTdevel- more profound conception of the law of development of these 

 opment. structures may satisfy us that it is in reality a physiological 



probability, apart from the evidence we have often derived from interest- 

 ing instances of its actual occurrence. It will be seen, when we treat of 

 the primitive appearance of the different secreting organs, that they are, 

 in reality, all evolved, as it were, from a common surface or membrane ; 

 that this primitive surface discharged, though perhaps in a confused way, 

 all their functions collectively ; and that in development the ruling idea 

 seems to be the separating out, or localizing upon a determinate spot or 

 region, structures which should have the duty, in a special manner at- 

 tached to them, of removing this or that particular substance, a central- 

 ization or concentration of action thus occurring. There is therefore 



