580 



MOVEMENTS OF THE SPLEEN. [BOOK n. 



A ' spleen curve ' (Fig. 109) taken in the same way as a 

 4 kidney curve ' does not, in the dog at all events, shew varia- 

 tions in the volume of the spleen corresponding with the pulse 

 waves. The kidney curve, as we have seen ( 330), gives 

 clear indications of each heart-beat, but the spleen curve shews, 

 besides the larger waves of which we shall speak directly, only 

 undulations due to the respiratory movements; and these, always 

 very slight, are sometimes not visible. In other words, the 

 spleen does not expand with the increase of blood-pressure 

 occurring in the splenic arteries after each heart-beat. More- 

 over when the supply of blood to the spleen is wholly and 

 suddenly cut off, as by clamping the aorta, the spleen curve 

 sinks very slowly, shewing that the spleen is diminishing in 

 volume not suddenly but very slowly. The pathway of the 

 blood through the splenic reticulum is peculiar; and increase 

 or decrease in the volume of the spleen means more or less 

 blood held in the spleen pulp, not necessarily a greater or less 

 flow of blood through the organ. 



FIG. 109. NORMAL SPLEEN CURVE FROM DOG. (Roy.) 



The upper curve is the spleen curve shewing the rhythmic contractions and 

 expansions ; the smaller waves are due to the respiratory movements. The 

 lower curve is the blood-pressure curve, and the point a of the spleen curve 

 corresponds in time to the point b of the blood-pressure curve. The marks on 

 the time curve below indicate seconds. 



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 expansions, though not always present, frequently make 

 their appearance, 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 contractions, with intervening relaxations, 



