1894.] the Force of Gravity on the Circulation. 193 



it lias been curiously neglected by physiologists. So far as my 

 researches into the history of the subject go, the mere fact that the 

 feet-down position lowers arterial pressure, and that the feet-up posi- 

 tion heightens it, is almost all that has been determined. 



In 1885, Hermann placed the subject in the hands of two pupils, 

 Blumberg and Wagner, with the object of investigating the dynamic 

 and hydrostatic effects of gravity on the circulation. 



The hydrostatic moment is the altered relationship of level between 

 the given spot on the artery (where the manometer is placed) and the 

 rest of the vascular system. 



The dynamic moment is the altered relation between pressure and 

 resistance produced indirectly by the change of position on the heart- 

 beat, the filling of the heart, the vaso-motor nerves, &c. 



Hermann instructed his pupils to find the indifferent point of the 

 circulatory system, in order that the hydrostatic effect might be 

 eliminated and the dynamic effect alone studied. 



Blumberg and Wagner determined the indifferent point by filling 

 the circulatory system of the dead animal with salt solution and 

 then by shifting the position of the axis round which the body was 

 turned. 



I have found that on attempting, according to Wagner's method, to 

 fill the circulatory system of the dead animal with salt solution, the 

 arterial part of the system does not remain filled, for the salt solution 

 rapidly leaks into the splanchnic venous area. By alternately placing 

 the animal with feet down or with feet up, a pumping action is pro- 

 duced which gradually forces the salt solution out of the arterial 

 system into the venous side, where it remains. The indifferent point 

 cannot, therefore, be found on the dead body. Further, if it were 

 possible to find the indifferent point on the dead body, the indif- 

 ferent point on the living body could not be deduced therefrom, 

 because such indifferent point depends on the coefficient of elasticity 

 which must constantly alter in the living animal with every altera- 

 tion of the arterioles by vaso-constriction or dilatation. 



As regards the dynamic effect of gravity on the circulation, there- 

 fore, the work of Blumberg and Wagner cannot be accepted. 



My attention was first drawn to the influence of gravity upon the 

 circulation by observations which I made upon the normal intra- 

 cranial tension in a patient of Dr. Glaze- Shaw. This patient had 

 been trephined, and Dr. Shaw asked me if I could estimate his 

 normal intra-cranial pressure. I did so by an adaptation of the 

 method for investigating intra-cranial pressure described by me in 

 the ' Proceedings of the Royal Society,' vol. 55. 



I found that the pressure was negative while the man sat up- 

 right, but that it became positive as soon as the head was bent 

 down towards the knees, and on any expiratory effort. The air- 



VOL. LVII. p 



