1889.] The Tnnervation of the Pulmonary Vessels. 375 



rose from 16 mm. to 22 mm. Hg, i.e., 6 mm. Thus in the latter case 

 the aortic rise was one-third of what it was in the previous experiment, 

 but the pulmonary rise was three times as great. 



This experiment then clearly demonstrates that the pulmonary 

 pressure is not dependent on the aortic rise, since the latter can be 

 obtained without the former, and a pulmonary rise, very considerable 

 in amount, can be obtained when the aortic rise is either small or 

 large. 



Hence this result points strongly to the conclusion that the vaso- 

 raotor centre can influence the pulmonary vessels directly. In the 

 light of Gaskell's work on the sympathetic, we naturally turn to the 

 roots of the upper dorsal nerves, and we are enabled to map out the 

 paths by which these vaso-motor nerves reach the lung. 



When the peripheral end of such a nerve as the 6th or 7th dorsal is 

 excited a rise of pressure in both the pulmonary and aortic system is 

 observed. The pulmonary rise, although considerable, e.g., 3 or 

 4 mm. Hg, is not out of proportion to the aortic rise which, with these 

 nerves, may be as much as 30 or 40 mm. Hg. On ascending, however, 

 very different results are obtained. Thus in one case the 5th dorsal 

 gave an aortic rise of 10 mm. Hg only, but the pulmonary rise was 

 3 mm. Hg. Clearly the latter was not a passive effect of the former. 

 In another case the 4th dorsal gave an aortic rise of 20 mm. Hg, and 

 a pulmonary rise of 4 mm. Hg. 



Perhaps, however, the most marked and conclusive result is seen 

 with the 3rd dorsal nerve. This nerve frequently causes no aortic 

 rise, and, indeed, sometimes actually a fall, e.g., 10 mm. Hg, but in both 

 these cases there is a distinct pulmonary rise of 3 or 4 mm. Hg. We 

 sometimes get such a fall in the aortic pressure accompanied by a 

 pulmonary rise with the 4th nerve and twice we have seen it with the 

 5th nerve. 



As a rule these effects cannot be obtained when the accelerators 

 produce marked effects, and hence no very definite results have been 

 obtained from stimulation of the 2nd dorsal nerve. Often, however, 

 the heart is already beating rapidly, so that irritation of the accelerator 

 nerves causes no further increase in rate, and it is under these circum- 

 stances that the pulmonary vaso-motor fibres can be most easily 

 demonstrated. Thus, as we pass from the 7th to the 2nd nerve, the 

 effect of their excitation on the aortic pressure diminishes as we pass 

 from below upwards, and the upper nerves may even cause a fall of 

 pressure in systemic circulation. On the other hand, the effect on the 

 pulmonary pressure seems to increase as we pass from below upwards. 

 Hence we may conclude that the vaso-constrictor fibres for the lungs 

 leave the spinal cord in the roots of the dorsal nerves from the 2nd 

 to the 7th. 



An attempt was made to separate the pulmonary nerves from the 



