262 EXPERIMENTAL INVESTIGATION OF THE ACTION OF MEDICINES. 



v Artificial Respiration in Manmials. — Artificial respiration is 

 chiefly used to keep an animal alive after it has been poisoned 

 with curare, for the purpose of rendering it perfectly still during 

 an experiment: or after the thoracic cavity has been opened for 

 observation or experiment on the viscera it contains. It is per- 

 formed by introducing a cannula into tlie trachea, and inflating 

 the lungs by means of a bellows connected with it by india- 

 rubber tubing. 



Fia. 129. 



A is a glass caniiula for artificial respiration, large enougli for a small dog. 

 A hole for the exit of expired air is seen in the side, b a metal one for a 

 rabbit. The hole for expiration is at the top, and not visible in the figure. 

 The lower part of the canniila can be turned round upon the upper at a joint 

 about one-third of the way from the top, not marked in the figure. The tube 

 •which conveys air can thus be brought from the side instead of the front. 



To introduce the cannula, an incision is made in the middle 

 line below the cricoid cartilage tlirough the skin and cutaneous 

 muscles ; the larger muscles lying along the side of the trachea 

 are separated from it by an aneurism-needle or the handle of 

 the knife, and a strong ligature is passed under it by an 

 aneurism-needle or forceps, care being taken to avoid the veins 

 which lie close to its posterior wall. A round or oval piece 

 must then be cut out of the front of it by the scissors or knife, 

 and the cannula introduced, and tied firmly in by the ligature. 



When the knee-shaped metal cannula is used, it is advisable 

 to push the heel of the cannula into the trachea, so that thfe 

 tube lies quite in its lumen. After the cannula has been tied 



