210 INFLUENCE OF NERVES ON THE SPLEEN. 



of systole and diastole may last for hours, and the two events together 

 occupy about one minute (Fig. 91). Changes in the arterial blood- 

 pressure have comparatively little influence on the volume of the spleen. 

 The rhythmical contractions, although modified, still go on after section 

 of the splenic nerves. This would seem to indicate that the spleen has 

 an independent (nervous) mechanism within itself causing its move- 

 ments.] 



Influence of Nerves. Section of the splenic nerves causes an 

 increase in the size of the spleen ; and when the nerves at the hilum 

 are extirpated it swells and assumes a deep piirple colour. The nerves 

 have their centre in the medulla oblongata, and so far they are com- 

 parable to vaso-motor nerves. Stimulation of the medulla oblongata, 

 either directly or by means of asphyxiated blood, causes contraction of 

 the spleen [hence, the spleen is " small and contracted " in death 

 from asphyxia.] The fibres proceed down the cord, and are probably 

 joined by other fibres derived from ganglion cells lying opposite the 

 first to the fourth cervical vertebi-re, which cells also act on the spleen. 

 The fibres leave the cord in the dorsal region, enter the left splanchnic, 

 pass through the semi-lunar ganglion, and thus reach the splenic plexus 

 (Jaschkowitz.) Stimulation of the peripheral ends of these nerves 

 causes contraction of the spleen, and so does cold applied to the spleen 

 directly or over the region of the organ. In this last case the result 

 is brought about reflexly. Section or paralysis of these nerves causes 

 dilatation, and so does curara or continued narcosis (Bulgak). [Botkin 

 found that the application of the induced current to the skin over the 

 spleen, in a case of leukaemia, caused well-marked contraction of the 

 spleen in all its dimensions ; the spleen becoming firmer, and its surface 

 more irregular. The result lasted much longer than the duration of 

 the stimulus. The same occurred in a case of enlarged lymphatic 

 glands. After a time the organ began to enlarge. After every stimu- 

 lation the number of colourless corpuscles in the blood increased, and 

 the condition of the patient improved.] 



[There is a popular notion that the spleen is influenced by the condition 

 of the nervous system. Botkin found that depressing emotions in- 

 creased its size, while exhilarating ideas diminished it. The causes of 

 these changes are referable not only to changes in the amount of blood 

 in the spleen, but also to the greater or less degree of contraction of 

 its muscular tissue. And it would appear that, like the small arteries, 

 the muscular tissue of the spleen is in a state of tonic contraction. The 

 size of the spleen may be influenced reflexly. Thus, Tarchanoff found 

 that stimulation of the central end of the vagus, when the splanchnics 

 were intact, caused contraction of the spleen, while stimulation of the 

 central end of the sciatic also caused contraction, but to a less degree. 



