328 THE POPULAR SCIENCE MONTHLY. 



law; on the normal pressure being restord, the gases with which it was 

 supersaturated pass into the free state. It is like drawing the cork of 

 a bottle of beer. The oxygen combines on the spot, but the nitrogeii 

 is at once set free, and carries with it carbonic acid in becoming dis- 

 engaged. Death is explained by the arrest of the circulation. 



But it must not be supposed that the action of compressed air is 

 harmless. If we subject a sparrow to a pressure of twenty atmos- 

 pheres, it will, after a few minutes, be seized with tremors, increasing 

 to most violent convulsions convulsions stronger than those of teta- 

 nus or of strychnine-poisoning and the bird soon dies. These terrible 

 symptoms are not the result of compression, as I have been able to 

 prove by two experiments. In the first place, they can be produced 

 at the pressure of five atmospheres, provided pure oxygen be used 

 instead of air, which latter has no special efiect at this pressure. 

 Secondly, they do not make their appearance if the air subjected to 

 twenty atmospheres' pressure is very poor in oxygen. 



Thus it is the oxygen that is to blame. Oxygen at too high a 

 degree of tension destroys animal life. Long I hesitated to character- 

 ize as a poison the " nursing father " of everything that lives, but 

 there was no help for it. Oxygen, which gives us life, slays also, 

 when administered in too strong a dose. I have had to study thor- 

 oughly this paradoxal poison to determine the difierent efiects of 

 varying doses, and its action upon our tissues. 



Here a new surprise awaited me. Having seen a sparrow killed 

 by oxygen, I supposed that this agent must have accelerated organic 

 combustion, thus consuming all the material which goes to maintain 

 the animal heat. But great was my astonishment when the ther- 

 mometer indicated in animals laboring under strong convulsions a fall 

 of several degrees in the temperature. The analysis of other phe- 

 nomena confirmed this first observation, and led me to the strange 

 conclusion that oxygen in excess kills by interfering with, arresting, 

 the intra-organic oxydation. 



The effects of this powerful agent begin to be distinctly felt at the 

 pressure of about five atmospheres. Perhaps they might be noticed 

 at a lower pressure, and I am inclined to attribute to this cause the 

 unfavorable symptoms presented by workmen who have spent several 

 months in compressed air ; but this is a complex problem. In any 

 case, if the necessities of industry subject men to pressures higher than 

 six atmospheres, they will be in danger not only at the instant of de- 

 compression, but even from the effects of the compression. 



Oxygen at a high tension kills not only the higher animals : it 

 acts alike on vertebrates and invertebrates, animals aerial and aquatic,, 

 plants and animals, big and little, even microscopic organisms. Its. 

 effects upon the latter are highly interesting. 



From the admirable researches of Pasteur it appears that the 

 phenomena of fermentation are of two kinds. One set of phenomena 



