372 Dr. J. R. Bradford and Mr. H. P. Dean. [Feb. 21 



a fall of aortic pressure from 105 mm. to 52 mm. Hg was accompanied 

 by a pulmonary fall of only 2 mm. Hg. 



Thus in two different animals sensibly the same effects were pro- 

 duced in the pulmonary pressure in opposite directions by practically 

 equal changes of pressure in opposite directions produced in the aortic 

 pressure. 



II. Results obtained by Excitation of the divided Spinal Cord. 



Excitation of the lower end of the divided cord produces an enor- 

 mous rise of general blood-pressure, but the accompanying rise of 

 pulmonary pressure is not only always small but it is frequently 

 absent. 



Thus in one case stimulation for 38 seconds caused a rise of general 

 blood- pressure amounting to 180 mm. Hg, and the simultaneous pul- 

 monary rise was 6 mm. Hg, This is an extreme case. In many 

 instances the pulmonary rise was less than this, even when the aortic 

 rise was quite as marked. In this case the aortic pressure rose from 

 52 mm. Hg to 232 mm. Hg, and the pulmonary pressure from 20 mm. 

 Hg to 26 mm. Hg, thus although the aortic pressure was quadrupled, 

 the pulmonary pressure was only raised, by less than one-third of 

 its previous amount. 



III. Results obtained by Compression of Thoracic Aorta. 



When this vessel is compressed about the middle of the dorsal 

 region by the finger introduced through the wound, the aortic pres- 

 sure measured in the carotid undergoes a great and sudden rise, 

 followed on removing the finger by a transitory fall. If the compres- 

 sion, be maintained for only a short time, e.g., 10 seconds, then there 

 is no rise of pulmonary pressure, although, of course, the aortic 

 pressure will have been greatly augmented, in this case from 104 mm. 

 to 169 mm. Hg, a rise of 65 mm. Hg. 



If, however, the compression be maintained longer, then the pul- 

 monary pressure rises as we see from the following experiment : The 

 aorta was compressed for 30 seconds, and the aortic pressure rose from 

 71 mm. to 128 mm. Hg, and that in the pulmonary artery from 19 mm. 

 to 22 mm. Hg. 



In all three of the preceding series of experiments the pulmonary 

 rise is very small when compared with the enormous effects produced 

 in the aortic pressure. In all these cases the pulmonary rise was 

 roughly one-twentieth of the simultaneous rise in the systemic cir- 

 culation. Not only is the rise of pulmonary pressure small when 

 compared to the aortic rise, but the actual pulmonary rise is but a 

 small fraction of the total pulmonary pressure. Thus, although some 

 of the above methods may double or even quadruple the aortic pressure, 



