Studies of the Pulmonary Circulation

The question of whether or not the blood-vessels of the pulmonary circulation are under the control of the central nervous system has been a subject for difference of opinion for many years. Several years ago I published ( I ) the results of some experiments bearing upon this problem, which led me to a belief in the existence of a vasomotor supply to the lesser circulation. Since then I have carried on further investigation of the pulmonary circulation, with especial reference, however, to the effects of drugs upon it. The results which I have obtained in this second series of experiments have strengthened the conviction obtained from my first work on the subject. Before proceeding, however, with the report of my own experiments, I wish to call attention to the histological research of Dr. Karsner, published simultaneously with this paper. Dr. Karsner, who interested himself in this problem at m y suggestion, has succeeded in demonstrating, by a method of intra vitam staining with methylene blue, the presence of nerve filaments in the muscular coat of the pulmonary artery. This evidence seems to me of extreme importance. Brodie and Dixon brought forward as one of their arguments against the probability of a pulmonary vasomotor system, that they were unable to find, microscopically, any nerves in these vessels ; but as they themselves recognized, such negative evidence is not' of great weight, because the failure to find nerve filaments in the pulmonary arteries does not disprove their existence; on the other hand, a positive result is of much value. It is improbable that