214 KANSAS UNIVERSITY SCIENCE BULLETIN. 



as high as four to five atmospheres of air pressure, and are 

 most liable to dangerous effects while passing from the cais- 

 sons to the external air. Sudden variations of pressure are 

 far more dangerous than gradual alterations. There is at 

 this time danger of accident due to embolism, by disengage- 

 ment of the gases within the blood. When the changes of 

 pressure are gradually undergone the intrapulmonary and 

 extrathoracic pressures fall or rise together, and thus the 

 circulatory mechanism remains unaffected. In the post-mor- 

 tem records of cases in which death ensued from the effects 

 of caisson disease, according to Smith, the congestion of the 

 viscera, including the lungs, has been noted, and tends to 

 show that the effects of high oxygen tension are not directly 

 limited to the nervous system, as Bert believed. 



In the grasshopper we possess an animal that continues re- 

 spiratory movements when the structures that are homologous 

 to the lungs of higher forms are removed, so that the effect 

 of the high tension directly on the nervous system can be as- 

 certained. In the grasshopper we have, therefore, most favor- 

 able material with which to determine the question whether 

 it is the altered state of the blood, the lowered absorption of 

 the congested lung tissue, the indirect tension through the 

 blood, or direct influence on the nervous system, that pro- 

 duces convulsions in these animals under high atmospheric 

 pressure. 



This work was undertaken at the suggestion and under the 

 guidance of Prof. Ida H. Hyde, to whom I am under great 

 obligations for kind and valuable aid. 



The Influence on Respiratory Movements in Normal and Decapitated Im- 

 mature Grasshoppers (Nymphs) Subjected to a High Pressure, that Al- 

 ternated with Atmospheric Pressure. 



Table I gives the average results obtained from these ex- 

 periments. It was seen that normal and decapitated immature 

 grasshoppers placed under a pressure of about 200 pounds, or 

 thirteen atmospheres, continue their respiratory movements 

 at a reduced rate and force for about three days ; after that all 

 movements cease. If the animals are now transferred to 



7. Smith, J. Lorain : Journal of Physiology, 1899, vol. XXIV, p. 34. 



