162 



THE MECHANISM OF THE CIRCULATION. 



hepatic vessels, and raised the pressure in both the portal vein and the 

 hepatic artery. 1 



The liver is exceedingly vascular, and forms an enormous reservoir 

 for the venous blood at periods when the diastolic filling of the right 

 heart is impeded ; for instance, during an intense muscular effort, or a 

 prolonged dive under water. The portal circulation is aided considerably 

 by the action of the respiratory pump. The abdominal wall compresses 

 the blood, while the thorax sucks the blood from the liver. The 

 circulation through the liver is thus greatly accelerated by muscular 

 exercise. 



The Splenic Circulation. 



The spleen must be looked upon as a sponge full of blood, the 

 trabecular of the spongework and the capsule being formed of muscular 

 tissue. Koy 2 found the spleen to be normally subject to regular alterna- 

 tions of volume (systole and diastole). These succeed one another in 

 the case of the dog and cat, without intermission, at regular intervals 

 of about a minute. In consequence of this power of contractility, the 

 circulation through the spleen is somewhat modified, and the spleen 

 may itself act as a pump to the portal system. 



The method employed for investigating the splenic circulation is that of 

 the plethysmograph. The first records were obtained by Koy, with the help of 

 a special hinged metal box or oncometer, in which the spleen was enclosed. 



The oncometer was, in its 

 turn, connected with a 

 piston recorder, termed 

 the oncograph. 



A suitable box for the 

 spleen, or for any other 

 separable viscus, can be 

 made of guttapercha. 3 It 

 should have flattened 

 edges, on which a flat plate 

 of glass accurately fits. 



The viscus is exposed 

 by a free abdominal inci- 

 sion, and placed within the 

 plethysmograph, the blood 

 supply to the organ pass- 

 ing over one side of the 

 box, which is made lower 

 than the others. The "lass 



Fig. 99. — Schiifer's visceral plethysmograph. 



cover is maintained in position with the help of indiarubber bands, and the 

 box is rendered air-tight by a free application of thick vaseline. Any gap 

 at the side of the vessels is plugged with cotton-wool soaked in vaseline. 

 A tube leads from the plethysmograph, and this is connected by an india- 

 rubber tube with a recording tambour or a piston recorder. The whole 

 apparatus is filled with air. 



Fig. 100 shows a typical spleen tracing. Two splenic contraction 

 waves are visible, and upon these are seen the respiratory and cardiac 

 undulations of arterial pressure. 



1 Arch, dephysiol. norm, etpath., Paris, 1897, pp. 434, 448. 



2 Roy, Journ. Physiol., Cambridge and London, 1880-2, vol. iii. p. 203. 



3 Schafer and Moore, Journ. Physiol.. Cambridge and London, vol. xx. p. 5. 



