INFLUENCE OF NERVES ON THE SPLEEN. 211 



It is quite certain that all the phenomena are not due to the action of 

 vaso-motor nerves on the splenic blood-vessels. There is a certain 

 amount of independent action of the muscular fibres of the organ, and 

 it is not improbable that the innervation of the spleen is similar to the 

 innervation of arteries, and that it has a motor centre in the cord 

 capable of being influenced by afferent nerves, and sending out efferent 

 impulses.] 



[Roy confirmed most of these results, and found that stimulation of 

 (1) the central end of a sensory nerve, (2) of the peripheral ends of 

 both splanchnics, (3) of the peripheral ends of both vagi, caused 

 contraction of the spleen. But even after section of the splanchnics 

 and vagi, stimulation of a sensory nerve still caused contraction, so 

 that there must be some other channel as yet unknown. Boche- 

 fontaine found that electrical stimulation of certain parts of the cortex 

 cerebri produced contraction of the spleen.] Sensory nerves seem to 

 occur only in the peritoneum covering the spleen. 



Pressure on the splenic vein causes enlargement of the spleen (Moslec) ; hence, 

 increased pressure in this vein (congestion of the portal vein, cessation of haemor- 

 rhoidal and menstrual discharges) also causes its enlargement. With regard to the 

 action of "splenic reagents," such as Quinine, on the contraction of the spleen, 

 Binz is of opinion that this drug retards the formation of the colourless blood-cor- 

 puscles, so that its chief function is interfered with and the organ becomes less 

 vascular. It is not definitely decided, however, whether it is contraction or dilata- 

 tion of the spleen that alters the proportion of red and white corpuscles in the blood. 



Splenic Tumours. The increase in size of the spleen in various diseases early 

 attracted the attention of physicians. The healthy spleen undergoes several varia- 

 tions in volume during the course of a day, corresponding with the varying activity 

 of the digestive organs. In this respect the spleen resembles the arteries. In 

 many fevers the spleen becomes greatly enlarged, probably due to paralysis of its 

 nerves. It is greatly increased in intermittent fever or ague, and often during 

 the course of typhus. When it becomes abnormally enlarged, and remains so after 

 repeated attacks of ague, it is greatly hypertrophied and constitutes "ague cake." 

 In cases of splenic leuksemia it is greatly enlarged, and at the same time there is a 

 great increase in the number of colourless corpuscles in the blood, and also a 

 decrease of the coloured ones (p. 23). 



II. The Thymus. 



During foetal life this gland is largely developed, and it increases during the first 

 two or three years of life, remaining stationary until the tenth or fourteenth year, 

 when it begins to atrophy and undergo fatty degeneration. [The degeneration 

 begins at the outer part of each lobule and progress inwards (His).] 



Structure. [" It consists of an aggregation of lymph-follicles (resembling the 

 glands of Peyer) or masses of adenoid tissue held together by a framework of con- 

 nective tissue which contains blood-vessels, lymphatics, and a few nerves (Fig. 92). 

 The framework of connective tissue gives off septa which divide the gland into lobes, 

 these being further subdivided by finer septa into lobules, the lobules being separated 



