1889.] The Innervation of the Pulmonary Vessels. 371 



operative procedure described above. The aortic pressure must fall very 

 low indeed for the pulmonary pressure to be appreciably diminished 

 in amount. The following is an instance bearing out the truth of this 

 statement. 



Section of spinal cord at level of seventh dorsal nerve caused the 

 aortic pressure to fall from 106 mm. Hg to 52 mm. Hg. The 

 pulmonary pressure fell from 16 mm. to 14 mm. Hg. Thus, while 

 the aortic pressure fell to half its previous height, the pulmonary 

 pressure only diminished by one-eighth of its previous amount. 



Artificial inflation of the lungs causes a rise of pressure in both 

 systems followed by a fall during the subsequent expulsion of the 

 injected air. The pulmonary rise is more sudden and marked in 

 character than the aortic rise, but the rise and fall of pressure in the 

 two vessels are, as far as can be determined, quite synchronous. 



The effect of artificial inflations is the same, whether the vagi are 

 intact or whether they have been previously divided. 



We will now turn our attention to the effects produced on the 

 pulmonary blood- pressure by a sudden increase in the aortic pressure. 

 It is evident that this rise of pressure in the systemic circulation 

 must be produced in such a way as to avoid stimulating, if possible, 

 the vaso-motor centre reflexly, although, as we shall see later on, the 

 results obtained by reflex excitation are also valuable in deciding this 

 question. 



Three methods have been used by us to produce a large rise of 

 blood-pressure in the systemic circulation, and so to determine the 

 passive effect of this rise on the pulmonary circulation. They are as 

 follows : 



I. The excitation of the peripheral end of a divided splanchnic. 



IT. The excitation of the lower end of the spinal cord divided in 

 the middle of the dorsal region, and care being taken that no spread- 

 ing of the current to the central end occurs. 



III. Compression of the thoracic aorta. 



I. Results obtained by Excitation of the Peripheral Jllnd of a divided 



Splanchnic. 



The rise of systemic blood-pressure is of course considerable, in many 

 cases it is doubled. The rise of pressure in the pulmonary artery is 

 not, however, very marked. Thus in one case an excitation lasting 

 48 seconds produced a rise of aortic pressure amounting to 54 mm. Hg. 

 The accompanying rise of pulmonary pressure was only 3 mm. Hg. 



The aortic pressure was rather more than doubled, having risen 

 from 50 mm. Hg to 104 mm. Hg, on the other hand, the pulmonary rise 

 was from 13 mm. Hg to 16 mm. Hg, the mean rise being, however, 

 2-5 mm. Hg. 



These results are curiously similar to those mentioned above, where 



