PRELIMINARY OPERATIONS 291 



lapse air will be drawn into the chest from the tambour 

 and the pointer will descend. If the bronchial muscles 

 contract or dilate the extent of this movement will be cor- 

 respondingly decreased or increased. The extent of ex- 

 pansion or contraction of the lungs can be controlled by 

 the screw clamp on the tracheal cannula (if the volume of 

 air delivered by the respiration machine at each inflation 

 cannot be independently controlled). The extent of move- 

 ment of the tambour pointer, i. e., of the amount of air en- 

 tering or leaving the tambour bowl, can be controlled by 

 the screw clamp on the ' ' inlet ' ' of Fig. 255. 



If negative pressure is used this is applied only after the 

 dog is pithed (this being determined by the administration 

 of the ether which is better done by positive artificial respi- 

 ration). Figure 257 shows the way to arrange the tubes to 

 the apparatus. In this case the tube to the recording tam- 

 bour is attached to the side tube (or better the end) of the 

 tracheal cannula (the ether bottle is removed, for it is no 

 longer necessary as the animal will then be pithed). The 

 other opening of the tracheal cannula carries a piece of 

 rubber tubing and a screw clamp. This clamp is used to 

 regulate the facility with A\ r liich air passes into and out of 

 the trachea and lungs. This regulates the size of the tam- 

 bour stroke on the drum. Closing the clamp down in- 

 creases the amplitude of the tambour stroke; opening the 

 clamp decreases the stroke. The attachment of the tam- 

 bour here and the removal of the ether bottle can be done 

 only after the animal is pithed. 



When the apparatus is adjusted pith the animal. To do 

 this consult Figs. 258, 259, 260, 261, and 262. 



Unfasten the dog's head and turn it on the left side. 

 The anesthetist watches carefully to see that the chest or 

 trachea is not compressed and that the animal gets suf- 

 ficient air while this part of the operation is performed. 

 With a scalpel make a median incision over the skull and 

 with large tin snips cut the skin away in a V-shaped area 



