778 MOVEMENTS OF THE SPLEEN. [BOOK n. 



Of special interest are the large slow variations of volume 

 which, besides the respiratory undulations, the spleen curve usually 

 shews, as seen in the figure. Rhythmic contractions and ex- 

 pansions, though not always present, frequently make their appear- 

 ance, each contraction with its fellow expansion lasting in the cat 

 and dog about a minute, and recurring with great regularity for a 

 long time ; and besides these the volume varies widely from time 

 to time. There can be little doubt but that the rhythmic 

 variations in volume are due in these animals to rhythmic con- 

 tractions, with intervening relaxations, of the muscular trabeculae 

 and capsule ; the slower variations are also probably due to the 

 same cause. In many animals the contractility of the splenic 

 tissue is shewn by the white lines of constriction which appear 

 when the electrodes of an induction machine in action are drawn 

 over its surface ; and similar lines may be produced by mechanical 

 stimulation with the point of a needle. So that the spleen in 

 these animals may be considered as a muscular organ, now ex- 

 panding to receive a larger quantity of blood and now contracting 

 to drive the blood on to the liver. When the muscular elements 

 are scanty in or absent from the capsule and trabeculae, the 

 expansion and contraction of the whole organ must depend alone 

 or chiefly on variations in the width of the supplying arteries. 

 We have evidence moreover that the muscular activity of the 

 spleen, whether of the muscular capsule and trabeculse and arteries 

 combined or of the latter alone, is under the dominion of the 

 nervous system. A rapid contraction of the spleen may be brought 

 about in a direct manner by stimulation of the splanchnic or 

 vagus nerves, or in a reflex manner by stimulation of the central 

 end of a sensory nerve ; it may also be caused by stimulation 

 of the spinal bulb with a galvanic current or by means of 

 asphyxia. Though the matter has not yet been fully worked 

 out, we have already sufficiently clear indications that the flow 

 of blood through the spleen is, through the agency of the nervous 

 system, varied to meet changing needs. At one time a small 

 quantity of blood is passing through or is being held by the 

 organ, and the metabolic changes which it undergoes in the 

 transit are comparatively slight. At another time a larger 

 quantity of blood enters the organ, and is let loose, so to speak, 

 into the splenic pulp, there to undergo more profound changes, 

 and afterwards to be ejected by the rhythmic contractions of the 

 muscular trabeculae. 



It is further obvious that these changes going on in the spleen 

 must have an important influence on the changes going on in the 

 liver; it cannot be of indifference to the- latter organ whether a 

 relatively small quantity of blood, relatively little changed, reaches 

 it from the spleen, or whether it receives a relatively large quantity 

 of blood, profoundly altered by the changes which it has undergone 

 in the spleen pulp. 



