1891. J T/ie Physiological Action of tie Paraffinic Nitrites. 317 



It is well established that small doses of amyl nitrite canse a fall of 

 blood pressure, resulting chiefly, if not entirely, from a powerful 

 dilatation of the arterioles, reducing peripheral resistance to a great 

 extent. Two distinct views have been advanced as to the cause of 

 the dilatation. Filehne maintains that his experimental results de- 

 monstrate the dilatation to be due, not to a local action on the walls 

 of the vessels, but to the direct action of the nitrite on the vaso-motor 

 centres. On the other hand, Brunton, and also Mayer and Priedrich, 

 believe they have shown that the dilatation is the result of a direct 

 action on the walls of the vessel, and is independent of any effect on 

 the central nervous system. 



After discussing the experiments of Filehne, Branton, and Mayer, 

 an account is given of the experiments made by the authors to eluci- 

 date this question. These were made with cats, but control experi- 

 ments with rabbits afforded the same results. In the first series the 

 head of the animal was entirely cut off from the circulation, yet inha- 

 lation of pure amyl nitrite (-sV-b. c.c.) caused a rapid fall of pressure, 

 the lowest point reached exactly corresponding with that noticed in 

 an immediately preceding experiment, in which the head was included 

 in the circulation. In the second series all the arteries passing to the 

 head were temporarily ligatured, and salt solution containing dis- 

 solved amyl nitrite (gVth c.c.) injected through the distal end of the 

 carotid artery, one of the jugular veins being opened so as to admit 

 of an escape of blood and hinder the production of a possibly 

 abnormal intravasealar tension in the brain. The same effect was 

 constantly observed ; the blood pressure rose, and not until the clamps 

 were removed did the fall of pressure of the usual character occur, 

 ["here is thus no indication of the characteristic nitrite effect, so long 

 is the vessels are ligatured, although the nitrite must have passed to 

 the medulla oblongata by vascular anastomosis, and therefore to the 

 chief vaso-motor centre. By the injection of Berlin blue, it was 

 demonstrated that access could be gained to the medulla through 

 this channel. The conclusion that the nitrite effect is the result of an 



3tion on the vessels, and not on the central nervous system, was con- 

 firmed by observations on the effect produced by nitrites after 

 splanchnic stimulation and section. Splanchnotomy is attended 

 with a considerable reduction of pressure, and if nitrite be admi- 

 nistered when this is at its minimum, a further redaction occurs, 

 which, however, is not so great as that observed before section. But 

 if administration of nitrite be delayed until the occurrence of one of 

 the temporary elevations of pressure which are observed from time to 

 time, the fall of pressure closely approximates to that produced before 

 splanchnotomy. Simultaneous splanchnic stimulation and nitrite 

 inhalation also cause a normal fall in pressure. 



In experiments with the human subject, an accurate record was 



