554 PHYSIOLOGY CHAP. 



Roy was able by the plethysmographic method, ingeniously 

 modified and applied to the spleen in situ, to study the automatic 

 variations in volume of this organ. He showed that the spleen of 

 dogs and cats presents periodic contractions and expansions 

 lasting in all for about a minute, independent of the slow 

 oscillations of arterial pressure, and therefore of the dilatations 

 and constrictions of the arteries, which must accordingly be 

 referred to the periodic contractions and expansions of the muscle 

 cells of the capsule and trabeculae. The spleen of these animals 

 is therefore a muscular organ which rhythmically expands to 

 receive an increased amount of blood, and rhythmically contracts 

 to expel a considerable part of the blood which it contains, in the 

 direction of the liver. During its expansion the blood which has 

 been driven out into the reticulum of the splenic pulp, and is at 

 rest there, probably undergoes important metabolic changes; 

 during contraction the blood which has suffered these changes, 

 and many of the mobile elements that lodge in the areoli 

 containing the pulp, and the follicular tissue of the Malpighian 

 corpuscles, are driven out through the efferent vessels of the 

 organ. 



The muscular activity of the spleen, whether of the muscles of 

 the capsule and trabeculae or of the vessels, is regulated and 

 controlled by the nervous system. A pronounced and more or 

 less rapid contraction of the spleen can be obtained by the 

 electrical excitation of the spinal bulb, the upper cervical cord, 

 left splanchnic, semiluiiar ganglion, and lastly the nerve plexus to 

 the spleen (Tarchanoff). The same effect can be obtained reflexly 

 by the electrical excitation of a sensory nerve or of the central 

 end of the vagus. The contraction of this organ during asphyxia 

 (as also in strychnine or strong quinine poisoning) is also due 

 to excitation of the nervous system, which governs the muscles of 

 the spleen. Section of the splenic nerves or their paralysis from 

 any cause induces the opposite effects, i.e. the passive enlargement 

 of the organ. 



According to Bulgak (1877), the reflex and motor centres for 

 the muscles of the spleen lie in the cord between the first and 

 fourth cervical vertebra, while lower down, as far as the eleventh 

 dorsal vertebra, there are only the afferent and efferent nerve 

 fibres to the spleen. Schafer and Moore substantially confirmed 

 these results. 



In view of the marked difference in volume which the spleen 

 exhibits owing merely to fluctuation in the amount of blood that 

 collects in it, certain physiologists, including Briicke, have looked 

 upon it as a diverticulum capable of modifying or influencing the 

 circulation of the other abdominal organs, notably the stomach 

 and the liver, in various ways. This idea is founded on the 

 anatomical fact that the splenic artery and the gastric and 



