212 KANSAS UNIVERSITY SCIENCE BULLETIN. 



valuable for experiments on respiration. Since respiratory 

 movements continue in the grasshopper, even after removal 

 of the viscera and trachea, it is possible to study the effects 

 of pressure acting directly on the nervous system, as well as 

 upon the intact animal. 



The apparatus employed for securing high atmospheric 

 pressure consisted of a pressure pump run by a dynamo, 

 and an iron cylinder with tubular connections as illustrated 

 on plate XLI. The cylinder which contained the animals was 

 three feet long and six inches in diameter, painted white in- 

 side, and supplied with two valves. One valve was connected 

 through a pressure gauge to the pressure pump, and the other 

 served for the exit of the air. The end lids of the cylinder 

 contained heavy glass windows through which light was re- 

 flected into the cylinder. The lids were closed air-tight by 

 iron caps that were secured in place by rivets, and all joints 

 were packed with rubber washers. An open glass tube that 

 contained potassium hydroxide was placed in the cylinder to 

 absorb the carbon dioxide. When studying the effects of low 

 pressure, the grasshoppers were placed in long test-tubes that 

 were connected air-tight to a Sprengle pump that gradually 

 exhausted the contained air. 



The material employed in the experiments consisted of dif- 

 ferent species of both spring and autumn, adult and imma- 

 ture grasshoppers, decapitated, and abdominal parts both with 

 and without the viscera and tracheal tubes. In the latter 

 the nerves were directly exposed to the pressure. 



According to Paul Bert,* the effect arising from variations 

 in barometric pressure on all living organisms is entirely the 

 result of the tension at which the oxygen is maintained under 

 various atmospheres ; and he has called attention to the fact 

 that, at a certain pressure, oxygen is not only not beneficial, 

 but, on the contrary, remarkably toxic. By exposing an 

 animal to four atmospheres of oxygen, for instance, the same 

 effect is produced as that caused by increasing the barometric 

 pressure of the air twenty times. Bert found that in small 

 birds exposed to three and one-half atmospheres of oxygen, 

 that is, seventeen and one-half barometric pressure of air, 



4. Bert, Paul E.: Comptes rendus de rAcademie des Sciences, 1873, vol. LXXVI. p. 443. 



