EFFECT OF VOMITING, 641 



factor, viz., the want of true vocal cords, and the consequent 

 difficulty of greatly increasing the intra-thoracic pressure, is 

 also a factor which ought not to be entirely disregarded. We 

 Imve made some experiments on the intra-thoracic pressure in 

 vomiting ; these were performed by narcotizing an animal with 

 ether, passing the arms of a T-shaped cannula upwards and 



Fig. 216. — Chaet A.— Eetching movements of cat, showing sustained intra, 

 tracheal pressure of 125 mm. mercury. 



Fig. 217. — Chart B. — Vomiting movements of same, showing resistance to 

 intra-tracheal pressure yielding at a? to 31 mm. mercury. 



downwards into the trachea, the cross-limb of which was con- 

 nected with a manometer. Sulphate of zinc was then injected 

 into the stomach, and the action of the anaesthetic was 

 diminished to the same point as in surgical operations where 

 vomiting occurs before the return of consciousness. The results 

 will be seen from the portions of the curves which were obtained 

 and which we here append. 



The middle curve was merely of retching. 



The secondary waves arise from mercurial oscillation. 



By the same kind of experiment it was proved that vomiting 

 was still possible when the projecting arm of the T-cannula was 

 unconnected with the manometer, and left open, but in this 

 case vomiting occurred with much greater difficulty than when 



2 T 



