492 Dr. J. B. Hicks. On the Supplementary Forces [Apr. 24, 



the button in the centre attached to the tambour fairly touching the 

 abdominal wall. On revolving the drum attached, a well marked 

 tracing is obtained, showing the respiratory wave ; more marked in 

 the male, but almost always well pronounced in the female. The 

 height of these waves, of course, marks the difference of the elevation 

 of the centre of the area and the circle described by the three legs 

 before mentioned, the amount indeed of the bulging of that portion. 

 By this arrangement the effects of the various movements of the body 

 can be also registered with great ease, so far as these movements 

 compress the walls of the abdominal cavity. 



But although the abdominal walls in front yield, yet the descent of 

 the diaphragm, which accompanies the inspiratory act, must put 

 pressure on the contents of the abdomen: and thus tension is created, 

 which is in a certain degree lessened — 1st, by the yielding of the walls 

 just mentioned, and, 2nclly, by the escape of blood from the vessels 

 within the cavity of the abdomen ; and this would be more marked in 

 the case of the venous blood. 



In the case of the arterial blood, the pressure would tend both up- 

 wards and towards the heart, and downwards towards the lower ex- 

 tremities and the abdominal walls. The movement towards the thorax 

 would probably be but slight, yet it would to a certain extent add 

 somewhat to the arterial tension, noticed as commencing at the be- 

 ginning of inspiration. The other, the downward movement, acting* 

 in the direction of the arterial current, would increase also the arterial 

 tension in the lower extremities and abdominal walls. But upon the 

 venous system the effect would be greater. 



1st. Upon the systemic its effects would be cut off in the downward 

 direction by the valves, though this would, tend to increase the venous 

 tension in the lower extremities. But this probably would be soon 

 neutralized, or nearly so, by the freedom which the incipient vacuum 

 caused by the expansion of the chest gives the blood to enter the 

 heart. But the pressure caused by the descent of the diaphragm 

 tends to press the blood in the vena cava also upwards, thus facili- 

 tating the flow in the natural direction ; but any tension to which the 

 vessel is subjected is probably immediately or simultaneously relieved 

 by the suction-action of the chest, which is well known to diminish 

 considerably the blood-pressure in the large veins close to the thorax 

 during the inspiratory movements. That this pressure of the dia- 

 phragm on the abdominal contents nearly if not quite balances the 

 suction- action, is shown by the fact that in the sciatic vein the 

 diminution of the blood-pressure during inspiration is not observed. 



2nd. The portal system is subjected likewise to pressure, and its 

 contained blood would tend to both its incipient and terminal capil- 

 laries ; and the resultant would be to facilitate its movement towards 

 the area of least resistance, namely, towards the heepatic veins. 



