201 



CHAPTEE XIX 



DEMONSTRATION OF THE NERVOUS REGULATION OF RESPIRATION. 

 THE STETHOMETER AND PNEUMOGRAPH 



In a previous experiment, p. 168, we saw how we could record the 

 respiratory rhythm in an animal by the aid of a tambour resting on 

 the thorax or abdomen. This method gives us all that is required so 

 far as the main details of time of inspiration and expiration and rate 

 of breathing are concerned, but we also require some method that will 

 give us a means of recording these same points, and in addition the 

 depth of breathing with some greater accuracy. One method that 

 has been adopted is to make the animal inspire from a large glass 

 vessel which is placed in communication with a tambour, so that 

 changes of pressure inside the vessel cause movements of the tambour 

 lever. Each inspiration causes a fall in pressure in the glass chamber, 

 and therefore a fall of the tambour lever. For this method it is not 

 necessary to have the vessel completely closed. The air must also 

 be frequently renewed. 



Another method that has been largely employed is to introduce 

 one end of a stiff lever so as to lie between the liver and the under 

 surface of the diaphragm. The lever moves about an axis near to 

 this end, so that all that is necessary is to record the movements of 

 the free end of the lever. This is usually carried out by attaching it 

 to a writing lever by a fine thread. 



In the case of the rabbit we possess a further very convenient 

 and accurate method, for there exists in this animal a slip of the 

 diaphragm in the anterior mid-line which can be isolated without 

 opening the pleural cavities. A record of the movements of this 

 slip is the method employed in the following demonstration :— 



DEMONSTRATION. THE NERVOUS REGULATION OF 

 RESPIRATION 



A rabbit is anaesthetised with ether. By a median incision in the neck, 

 extending for about 1§ inches above and below the larynx, the two Tag] 

 are first isolated and threads passed under them. The superior laryngeal on 



