452 



SECRETION. 



[CHAP. xxxn. 



in the body as to have an external anatomical position, so as to be 

 able to set free the secreted product when formed. Some organs 

 of a strictly secreting kind, pour their material directly into the 

 blood. It appears most reasonable to regard the whole lymphatic 

 system as an apparatus of this description, calculated not merely 

 to restore to the circulating current the superfluous or altered 

 plasma, thrown by the capillaries into the interstices of the tissues, 

 but destined by its glandular parts especially to act on the passing 

 fluid, and to pour into it additional secreted matters, which pass 

 by the efferent vessels to blend with the general mass of blood. 

 The inner surface of the lymphatic vessels is here the external 

 free surface, to which we refer as that from which the secretion is 

 liberated.* 



Again, there are other organs, viz., the synovial and serous 

 membranes, which are usually and correctly classed as secreting 

 organs. They have been already described (vol. i. p. 126). The 

 fluid they secrete seems furnished for the purpose of lubricating 

 their surface, so as to facilitate motion. It, consequently, does not 

 leave the surface on which it becomes free, but remains in contact 

 with it, and only undergoes the same slow renewal and absorption, 

 as all other solids and fluids with which blood in motion is brought 

 into close contiguity. We have no reason to suppose that the 

 effusions on these surfaces suffer much deterioration by their con- 

 tinued contact. They appear to differ but slightly from the serum 

 of the blood, contain the same saline matters in solution, and in 

 nearly the same proportions. The epithelium of these surfaces is 

 no doubt concerned in furnishing these fluids, but exerts little 

 catalytic power over the liquor sanguinis, which, consequently, is 

 little altered by being secreted. Mr. Rainey has well pointed out 

 that the epithelium in certain situations is developed in a par- 

 ticular manner upon the projecting folds and fringes of synovial 

 membrane, known as glands of Havers; and has shown it to be 

 probable that the viscid synovia owes its origin chiefly to the sur- 

 face of these parts. He has found this disposition not only in 

 the joints, but also in the sheaths of tendons, and in the bursse 

 mucosse.t 



But, dismissing these structures, we arrive at that great system 



* This view results from Professor Goodsir's anatomical researches, and 

 from considerations which have been ably stated by Dr. Carpenter. See 

 ante, p. 275. 



t Proceedings of the Royal Society, May 7, 1846. 



