PHYSIOLOGICAL ACTION OF ORGANIC CHEMICAL COMPOUNDS. 153 



spoke in 1864 is a true excitement due to the influence excited by the agent 

 on the motor centres. I think, from my own sensations, it is rather due to an 

 indirect or mental impression, that it indicates a vehement desire to escape 

 from the influence of the agent, like the excitement of fear or frenzy. 



Let me from these points turn to the observations of the past year. I 

 observed long ago, in making dissections of the bodies of animals that had 

 died from amyl nitrite, that the condition of the lungs varied much, that 

 sometimes the lungs were of milky whiteness, sometimes of leaden hue, 

 and again of deep dark red hue. It occurred to me at last that these differ- 

 ences were not accidental, but that they depended upon the mode in which 

 the agent destroyed the life of the animal. Thereupon 1 made direct inquiry 

 into this subject, and was led to discover that I could, practically, modify the 

 circulation of the blood, passing over the lung from the right to the left 

 heart, as I pleased ; in other words, I learned that the vessels of the luugs 

 are influenced by the nitrite in the same manner as the vessels of the skin. 



The observation thus stated led me naturally a step further. I inquired 

 as to results of different temporary lesions that might be inflicted on the 

 pulmonary organs by the nitrite, and what extremity of lesion could be 

 recovered from under conditions favourable to recover3\ I commenced this 

 research in February last, and have carried it on without intermission from 

 that time : the results of the labour have been most instructive. 



There are four distinct conditions of lung producible by nitrite of amyl ; 

 there may be more, but I know of these : — 



1. If the animal be destroyed by an overwhelming dose of the agent, so 

 that it dies instantly, as it might die from sjoicope, the lungs are left 

 absolutely bloodless and of pure whiteness. The right side of the 

 heart is in this case paralyzed ; but exposed to the air immediately after 

 death it often recovers its power of contraction. In this instance the 

 death is reallj^ by syncope ; the nervous paralysis is extended immediately to 

 the heart, probably from paralysis of the sympathetic supply, and the right 

 ventricle failing to pour out its blood to the lung, the death is so instan- 

 taneous that there is no time left for the production of any organic change. 



2. If the death be comparatively slow, if it be preceded by a short interval 

 of muscular prostration, and if it occur from paralysis of the muscles 

 of respiration, then the lungs are left charged with dark tarry blood, 

 but they contain air and are free of congestion. Here the lungs and heart 

 have failed together, and the balance of the pulmonary circulation has been 

 fairly maintained. 



3. If the effect of the nitrite be more definitely prolonged, there is pro- 

 duced intense general congestion of the pulmonary vascular system, a con- 

 gestion so intense that the lungs, full of blood, clark and heavy, will not 

 float in water. The cause of death in this instance is progressive neural 

 paralysis of the pulmonary vessels ; it is the equivalent of congestion of the 

 lungs from long expose to extreme cold. 



4. The above may all be considered as acute changes in the pulmonary 

 structures, and the two first-named changes are immediately fatal. The 

 last need not be ; as it occurs from prolonged and siistained action of the 

 nitrite, in quantities insufficient to kill directly, the effects of sustained con- 

 gestion may be traced out from day to day for many weeks. 



To be accurate in the observations made on this subject, I constructed a 

 glass house or chamber of a capacity of three cubic feet, and so ventilated it 

 that the air could be kept charged with the vapour of the nitrite. In this 

 chamber rabbits and guineapigs were housed. They were carefully fed, 



