41 8 THE DUCTLESS GLAXDS. 



for a golden yellow, brown, or black colour; and, at length, 

 are converted into pigment-granules, which, by degrees 

 become paler and paler, until all colour is lost. The 

 corpuscles undergo these changes whether the heaps of 

 them are enveloped by a cell-wall or not. 



Besides these, its supposed direct offices, the spleen is 

 believed to fulfil some purpose in regard to the portal 

 circulation, with which it is in close connection. From the 

 readiness with which it admits of being distended, and 

 from the fact that it is generally small while gastric 

 digestion is going on, and enlarges when that act is con- 

 cluded, it is supposed to act as a kind of vascular reservoir, 

 or diverticulurn to the portal system, or more particularly 

 to the vessels of the stomach. That it may serve such a 

 purpose is also made probable by the enlargement which 

 it undergoes in certain affections of the heart and liver r 

 attended with obstruction to the passage of blood through 

 the latter organ, and by its diminution when the congestion 

 of the portal system is relieved by discharges from th& 

 bowels, or by the effusion of blood into the stomach. 

 This mechanical influence on the circulation, however, 

 can hardly be supposed to be more than a very subordinate 

 part of the office of an organ of so great complexity as the 

 spleen, and containing so many other structures besides 

 blood-vessels. The same may also be said with regard to 

 the opinion that the thyroid gland is important as a 

 diverticulum for the cerebral circulation, or the thymus 

 for the pulmonary in childhood. These, like the spleen, 

 must have peculiar and higher, though as yet ill-under- 

 stood, offices. 



