SECRETION. 



323 



undergoes in certain affections of the heart and liver, attended with ob- 

 struction 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. 



The spleen may be removed without any obvious ill effect. 



Influence of the Nervous System upon the Spleen. When the spleen is 

 enlarged after digestion, its enlargement is probably due to two causes, 

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



Fig. 230. Fig. 231. 



Fig. 230. Transverse section of a lobule of an injected infantile thymus gland, a, Capsule 

 of connective-tissue surrounding the lobule ; 6, membrane of the glandular vesicles ; c. cavity of 

 the lobule, from which the larger blood-vessels are seen to extend toward and ramify in the 

 spheroidal masses of the lobule, x 30. (Kolliker.) 



Fig. 231. Thymus of a calf, a, Cortex of follicle; 6, medulla; c, interfollicular tissue, 

 magnified about twelve times. (Watney.) 



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

 are doubtless 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 (1) by stimulation of the 

 spinal cord (or of the divided nerves) ; (2) reflexly by stimulation of the 

 central stumps of certain divided nerves, e.g., vagus and sciatic; (3) by 

 local stimulation by an electric current; (4) the exhibition of quinine and 

 some other drugs. It has been shown by the oncometer of Koy (fig. 307), 

 that the spleen undergoes rhythmical contractions and dilatations, due 

 no doubt to the contraction and relaxation of the muscular tissue in its 

 capsule and trabeculae. It also shows the rhythmical alteration of the 

 general blood pressure, but to a less extent than the kidney. 



