ROLLER : RESPIRATORY RESPONSES IN GRASSHOPPERS. 219 



external pressure ; but the normal dimensions were again 

 regained when they were subjected some time to a vacuum. 

 The respiratory movements ceased at the end of ten minutes, 

 and in some experiments before the end of six minutes, while 

 the pressure was being gradually decreased and a vacuum not 

 yet attained. 



In the last stages of respiratory activity there was a strong 

 launching forward, as if gasping for air, and the appendages 

 assumed a flexed or semiflexed position, in which they re- 

 mained. The heart was found beating after hours of expos- 

 ure to a vacuum, though respiration had stopped. 



It was seen from this series of experiments that November 

 grasshoppers cease respiratory movements as a vacuum is 

 produced, and that if they are kept in a vacuum seven hours 

 and then exposed to atmospheric air they will recover ; but 

 an exposure of eight hours to the vacuum proves fatal. 



CONCLUSIONS. 



It was believed by Paul Bert and Smith that the injurious 

 eff'ects on lung tissue and the nervous system, due to high 

 tensions of atmospheric pressure, are referable to the toxic 

 influence of oxygen at high pressure, which then acts as an 

 irritant, producing inflammation or pneumonia, and convul- 

 sions. Smith showed, furthermore, that if the pressure is 

 gradually raised, the onset of inflammation and convul- 

 sions is greatly postponed, and later he proved that it was 

 not alone the toxicity of the oxygen at high tension that was 

 responsible for the pathological conditions, but that the high 

 atmospheric pressure itself was injurious to the lung tissue 

 and nerve-cells. Related to the experiments on the influence 

 of high atmospheric tension is the question of caisson disease. 

 Post-mortem records of cases dying from this disease showed 

 congestion of the lungs. The workers are often under a 

 tension of 4 to 5 atmospheres. It has been believed that this 

 disease is produced rather by the sudden change from the 

 high to low pressure, but it is admitted that the risk of acci- 

 dent to workers is proportional to the time of exposure to 

 high pressure. 



The results obtained from a study of the influence of 



