RESPIRATION 69 



diminishes as the carbon dioxide is increased, down to a 

 miminum (at about 25 per cent. CO2). With further increase 

 of CO2, it then suddenly increases till it actually exceeds the 

 oxgyen consumption in C02-free air. Finally, after attaining 

 a maximum, the intake of oxygen rapidly falls to zero under 

 carbon dioxide narcosis. This surprising phenomenon sheds 

 a new light on the significance of the abdominal contractions 

 extensively studied by Babak (19 12) and regarded by him as 

 respiratory movements. Babak had shown that phenomena 

 analogous to Cheyne- Stokes breathing and asphyxia could be 

 induced by varying the contents of the inspired medium ; but 

 crucial evidence that such disturbances of the normal rhythm of 

 abdominal movements had any compensatory value was lack- 

 ing. In Dixippus, however, when the normally spasmodic 

 contractions of the rump and abdomen became rhythmical 

 in lack of oxygen or excess of carbon dioxide, the increased 

 rapidity of the movements corresponds with an increase in 

 oxygen consumption, and it is difficult to escape the conclusion 

 that they actively facilitate the renewal of air in the tracheal 

 system. There is, moreover, a correlation between the opening 

 and closure of the stigmata and the respiratory movements. 

 In Dixipus, according to the observations of Buddenbrock 

 and Rohr, the thoracic stigmata open with each expiratory 

 movement and close with relaxation of the abdominal muscle, 

 thus, seemingly, promoting the passage of a current of air 

 from behind forwards. 



Lee (1924), working on several other genera of Orthoptera, 

 has recently observed in their respiratory movements a definite 

 sequence of valvular motions of the thoracic and abdominal 

 spiracles (stigmata). According to Lee's account the external 

 valves or lips of the thoracic and first two pairs of abdominal 

 orifices of grasshoppers open when the abdomen enlarges and 

 close when it contracts. The orifices of the last six pairs of 

 abdominal spiracles are open during expiration and closed when 

 the abdomen enlarges. Hence if the abdomen of a normal 

 grasshopper is submerged while the head and thorax are 

 kept above the level of the water, minute bubbles escape 

 from the posterior abdominal spiracles ; when the whole 



