332 THE DUCTLESS GLANDS [CH. XXIII. 



these animals, cells are found in the spleen similar to those we have 

 described in red marrow, and called Ticematollasts. In these animals, 

 if the spleen is removed, the red marrow hypertrophies. 



(3.) There is reason to believe that in the spleen many of the red 

 corpuscles of the blood, those probably which have discharged their 

 office and are worn out, undergo disintegration ; for in the coloured 

 portions of the spleen-pulp an abundance of such corpuscles, in various 

 stages of degeneration, are found, and in those cases of disease in 

 which the destruction of blood-corpuscles is increased (pernicious 

 anaemia) iron accumulates in the spleen as in the liver. It was 

 formerly supposed that the spleen broke down the corpuscles and 

 liberated haemoglobin, which, passing in the blood of the splenic vein 

 to the liver, was discharged by that organ as bile-pigment. But this 

 is not the case; the disintegration does not proceed so far as to 

 actually liberate haemoglobin; there is no free haemoglobin in the 

 blood-plasma of the splenic vein. 



(4.) From the almost constant presence of uric acid, in larger 

 quantities than in other organs, as well as of the nitrogenous bodies, 

 xanthine and hypoxanthine, in the spleen, some share in nitrogenous 

 metabolism may be fairly inferred to occur in it. 



(5.) Besides these direct offices, the spleen fulfils some purpose 

 in regard to the portal circulation with which it is in close connec- 

 tion. 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 concluded, it is supposed to 

 act as a kind of vascular reservoir, or diverticulum to the portal 

 system, or more particularly to the vessels of the stomach. That it 

 may serve such purpose is also made probable by the enlargement, 

 which it undergoes in certain affections of the heart and liver, 

 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 the 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 

 function. 



Influence of the Nervous System upon the Spleen. When the 

 spleen is enlarged after digestion, its enlargement is due to two 

 causes : (1) a relaxation of the muscular tissue which forms so large 

 a part of its framework ; (2) a dilatation of the vessels. Both these 

 phenomena are under control of the nervous system. It has been 

 found by experiment that when the splenic nerves are cut the spleen 

 enlarges, and that contraction can be brought about by stimulation of 

 the peripheral ends of the divided nerves. If the splenic nerves are 

 not cut, contraction is produced by (1) stimulation of the spinal 

 cord ; (2) reflexly by stimulation of the central stumps of certain 



