CHAP, iv.] METABOLIC PEOCESSES OF THE BODY. 581 



of the muscular trabeculse 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 expanding to receive a larger quan- 

 tity 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 trabeculse, 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 sys- 

 tem. 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 

 medulla oblongata with a galvanic current or by means of as- 

 phyxia. 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 trabeculse. 



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. Some of 

 the changes taking place in the spleen are histological in 

 nature. 



373, When the so-called spleen pulp is examined under 

 the microscope, it is found to consist, besides the branched cells 

 and fibres constituting the reticulum, of cells which may be 

 described as partly red corpuscles and partly white corpuscles 

 or leucocytes. We spoke of the meshes of the reticulum as 

 being filled with blood; but it is obvious that the corpuscles of 

 the blood must move less readily through the labyrinth than 



