599 



that no increase of sensibility takes place, at least during several 

 hours. I then pump out the hydrogen, and inject atmospheric air, 

 and in a few minutes the posterior parts of the body become 

 hypersesthetic. 



When the posterior columns of the spinal cord have been divided 

 transversely, there is, as I found long ago, an excessive hyper- 

 eesthesia in all the parts of the body situated behind the section, 

 and also in some of the parts immediately above it. This hyper- 

 sesthesia begins almost at once after the operation, and increases for 

 many hours, and sometimes for one or two days. It diminishes a 

 little afterwards, and if there is no myelitis, it continues to exist, 

 though less than at first, for years after the operation. A part of 

 this hyperaesthesia (its great excess during the first hours and days), 

 I have recently found to depend chiefly upon the influence of the 

 oxygen of the air. If we perform the section of the posterior columns 

 of the spinal cord, and cover the wound immediately afterwards 

 with the apparatus above-mentioned, and pump out the air and 

 inject hydrogen, we find that there is a delay in the development 

 of hypersesthesia, and that it is never as considerable as when air 

 is in contact with the injured cord. If we replace the hydrogen 

 by air, there is a rapid increase of the hyperaesthesia, and there is still 

 more so if we inject pure oxygen. When the hypersesthesia has 

 once become excessive, hydrogen does not diminish it. 



If carbonic acid is injected, slight convulsive movements are pro- 

 duced, and sensibility soon diminishes. 



Analogous experiments on sensitive and motor nerves show that iu 

 them also an increase of the vital properties is produced by oxygen, 

 and that a diminution after an excitation is produced by carbonic acid. 

 Experiments on the abdominal sympathetic give similar results. 



Rolando and others have found that the gray matter which is in 

 the rhomboidal ventricle of the lumbar enlargement of the spinal 

 cord in birds, is not excitable either to give pain or produce move- 

 ment. I have ascertained that normally it is but little excitable, 

 but that when it has been exposed to the contact of air for some 

 10 or 15 minutes, it is extremely excitable, particularly for the pro- 

 duction of movements. This, perhaps, explains the curious dis- 

 turbance in the voluntary movements which I found some years ago 

 in birds, on which this gray matter had been simply laid bare. 



