THE VASCULAR GLANDS. 



goes 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 mechani- 

 cal influence on the circulation, however, can hardly be supposed to be 

 more than a very subordinate function. 



It is only necessary to mention that Schiff believes that the spleen 

 manufactures a substance without which the pancreatic secretion cannot 

 act upon proteids, so that when the spleen is removed the digestive action 

 of the pancreas is stopped. 



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



nomena 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 



means of a modification of the plethysmo- 



graph (Roy), that the spleen undergoes rhyth- 



mical contractions and dilatations, due no 



doubt to the contraction and relaxation of 



the muscular tissue in its capsule and tra- 



beculse. The gland also shows the rhythmical 



alteration of the general blood pressure, but 



to a less extent than the kidney. 



THE THYMUS. 



FIG. 255. Transverse section of a 

 lobule of an injected infantile thymus 

 S^nd. a, capsule of connective tis- 

 sue surrounding the lobule; 6, mem- 

 brane of the glandular vesicles; c, 

 cavity of the lobule, from which the 

 larger blood-vessels are seen to ex- 

 tend toward and ramify in the sphe- 

 roidal masses of the lobule, x 30. 

 (Kolliker.) 



This gland must be looked upon as a tem- 

 porary organ, as it attains its greatest size 

 early after birth, and after the second year 

 gradually diminishes, until in adult life hard- 

 ly a vestige remains. At its greatest devel- 

 opment it is a long narrow body, situated in the front of the chest behind 

 the sternum and partly in the lower part of the neck. It is of a reddish 

 or greyish color, distinctly lobulated. 



Structure. The gland is surrounded by a fibrous capsule which 



