332 The Circulation through the Dog’s Spleen 
spleen when it is injected into the artery of a live animal must be prac- 
tically instantaneous, paralyzing the muscle and fixing the blood cor- 
puscles in their natural channels. That the pulp of the spleen is found 
gorged with blood in this experiment is conclusive evidence in favor of 
an open circulation. 
The forces which drive the blood through the pulp are undoubtedly 
the arterial pressure, the elasticity of the reticulum and the contraction 
of the muscle of the spleen. Judging from the arrangement of the trabec- 
wlae and veins in distended spleens it is very apparent that the contrac- 
tion of the trabeculae have a decided influence in pulling the veins open. 
So when the muscle contracts it exerts a pressure upon the pulp more 
than it does upon the contents of the larger veins; in other words, the 
arrangement is such that the contraction of the muscle forces the flow of 
blood from the intralobular veins to the interlobular veins. When the pulp 
is compressed, however, the elasticity of the reticulum (1. ¢., p. 29) acts 
more upon the pulp than upon the capillary veins, again favoring the cir- 
culation from the pulp-spaces into the capillary veins. Therefore the ana- 
tomical and physiological arrangement is such that the contraction of the 
muscles of the trabeculae and capsule will press blood from the pulp into 
the veins without the aid of the arterial pressure. On the other hand it 
is through the arterial pressure that the pulp-spaces are filled when the 
spleen is relaxed, for it alone can overcome the elasticity of the reticulum. 
The arterial pressure itself is sufficient to carry on a complete circulation 
through the spleen, but the pulp-spaces can be fully emptied only by the 
contraction of the splenic muscle. The contraction of the splenic 
muscle has a tendency to close the capillary arteries while on the other 
hand with the aid of the elastic reticulum the capillary veins are pulled 
open. Therefore this contraction forces blood in one direction only. 
The conclusion to be drawn from this study is that the course of the 
red blood corpuscles is always through the pulp-spaces in passing from 
from the artery to the vein. I have been unable to gather any good evi- 
dence in favor of some closed capillaries, as suggested by W. Miiller, 
Miescher, Weidenreich and others. Thoma’s Zwischenstiick represents 
only the more direct pulp-space between the ampulla and the vein, which 
is best demonstrated when the rest of the pulp-spaces are gorged with 
blood. 
EXPLANATION OF PLATE I. 
Section of a spleen made oedematous by injecting chrome yellow suspended in 
gelatin into the vein. The artery was then injected with an aqueous solution of 
Prussian blue. The specimen was cut on the freezing microtome, tinged with picric 
acid mounted in glycerine. Enlarged 250 diameters. .A, artery; a, ampulla; 
V, vein. 
