ROLLER : RESPIRATORY RESPONSES IN GRASSHOPPERS. 213 



convulsions appeared in about five minutes, and if exposed 

 to the pressure longer, and then removed to atmospheric pres- 

 sure, the tetanic spasms continued until death. If the ten- 

 sion was raised at once beyond this, the birds died at once. 

 In a dog, the toxic effect lasted twenty-four hours after it was 

 removed from the high oxygen pressure. He concluded that 

 oxygen, at a certain tension, became toxic to nerve tissue. 



According to Verworn,^ pure oxygen at a pressure of more 

 than three atmospheres, or fifteen atmospheres of air, is fa- 

 tal to horaothermal animals, while, with ordinary air, the 

 same results appear at fifteen to twenty atmospheres. The 

 animals die of asphyxia and convulsions, exactly as when 

 oxygen is deficient and the production of carbonic acid is in- 

 creased. Muller*' found that at twenty atmospheres germi- 

 nation and putrefaction are arrested. Smith ^ discovered 

 that, when birds were exposed twenty-four hours to an oxy- 

 gen tension of 180 per cent., or nine atmospheres of air, 

 the lungs become inflamed and that the time of onset of the 

 inflammation is earlier the higher the tension. Oxygen 

 which, at the tension of the atmosphere, stimulates the lung 

 cells to active absorption, at higher tension acts as an irri- 

 tant, is toxic, and produces inflammation. He also ascer- 

 tained that there were two phases of oxygen effects, one 

 consisting in a slowly developing inflammatory state, seen 

 most prominently in the congestion of the lung tissue ; the 

 other a rapidly developing effect on the nervous system. A 

 tension of twenty atmospheres, for instance, gives rise to the 

 inflammatory effect in mice in five hours; and in birds, un- 

 der the same tension, in twelve minutes, to convulsions, due 

 to tetanic effects on the nervous system. This question is of 

 practical importance in connection with caisson and sub- 

 marine work and the therapeutical use of oxygen. 



According to records of men in caissons, engaged in severe 

 work under an oxygen tension of about two atmospheres, of- 

 ten some endure the exposure without severe effect, while in 

 others it has an effect on the lungs. They are occasionally in 



5. Verworn : Sitzungsbericht der koniglichen Preussischen Akademie der Wissenschaften 

 zu Berlin, 1896, p. 1243. 



6. MuUer, W. : Sitzungsbericht der koniglichen Akademie der Wissenschaften, Wien, 1858, 

 Bd. 33, p. 99. 



