370 Dr. J. B. Bradford and Mr. H. P. Dean. [Feb. 21, 



nerves between the spinal cord and the ligature, the peripheral ends 

 could be easily arranged for excitation. 



In this way the fibres of both anterior and posterior roots are 

 excited, but, as previously shown by one of us, no efferent vaso-motor 

 fibres can be demonstrated to exist in the posterior roots. Hence for 

 our purposes this mode of excitation is practically equivalent to 

 exciting the anterior roots alone, and inasmuch as a comparatively 

 long stretch of tough nerve can be obtained, the danger of the 

 exciting current spreading to the spinal cord, and so producing reflex 

 effects, is avoided. The nerves were excited on the right side, on the 

 same side as the uninjured lung. 



The two blood-pressure curves were recorded simultaneously on the 

 same blackened surface, together with a time tracing and a lever 

 marking the duration of the excitation. 



The anaesthetics used were chloroform and morphia, and after the 

 nerves had been prepared, a small dose of curare was injected, and 

 artificial respiration maintained before opening the chest to insert the 

 pulmonary cannula. 



Before describing the results following excitation of the upper 

 dorsal nerve roots, it will be necessary to describe shortly the relations 

 existing between the systemic and pulmonary blood-pressures, and 

 more especially what effects are produced on the pressure in the 

 pulmonary artery by sudden alterations of the blood-pressure in the 

 systemic vessels. It is necessary to do this, as otherwise in many 

 cases it might be urged that the effects of a given nerve excitation on 

 the pulmonary pressure were simply due to the reaction of the 

 pulmonary vessels to the accompanying carotid rise. In some cases 

 this objection has no force whatever, since there is no carotid rise or 

 there may even be a carotid fall. In other cases, e.g., in stimulation 

 of the fifth dorsal neive, there is often a rise of blood-pressure in both 

 vessels, and so we see how important it is to get a clear notion as to 

 what effect a given rise of arterial tension has on the pulmonary 

 blood-pressure. 



Before describing the results we have obtained in this direction, it 

 will be convenient to consider shortly the actual amount of the 

 pulmonary blood-pressure, and the manner in which it is influenced 

 by artificial inflation of the lungs. 



The pressure is found to vary between 16 mm. and 20 mm. of 

 mercury in different dogs, these being the animals we have always 

 used in our experiments. The pressure in the main artery is a few 

 millimetres higher than this. 



The pulmonary pressure is very constant in its height, not only in 

 the same animal during the course of an experiment, but also in 

 different animals. In this point it contrasts strongly with the aortic 

 pressure, since the latter is very variable in amount after the necessary 



