92 EXPERIMENTAL PHARMACOLOGY 



and the screw clamp on the straight end of the cannnla is 

 adjusted to make the dog breathe just enough ether to keep 

 the anesthesia constant (Fig. 89). The forceps beneath 

 the trachea are withdrawn and the aneurism needle is 

 hooked under the right carotid sheath which is lifted up 

 out of the wound (Fig. 89). "With a blunt-pointed probe 

 the sheath is opened and the carotid artery and vago-sym- 

 pathetic trunk are separated. A ligature is placed under 

 the nerve and tied loosely. A bull-dog clamp is placed on 

 the ends of this ligature (Fig. 90) which is now dropped 

 down beside the neck. Similarly with forceps two more 

 ligatures are placed on the carotid artery and tied loosely 

 (Fig. 90). It is extremely important that the student learn 

 to do these operations with his dissecting instruments 

 not ivith his fingers except to tie knots, etc. Many stu- 

 dents bring with them from their anatomy courses an ab- 

 surd notion that they should do most of their dissections 

 with their fingers. Learn to use your dissecting instru- 

 ments. That is the only royal road to first-class operative 

 success. Place a bull-dog clamp (serrefin) on the carotid 

 low down in the neck and tie tightly the upper ligature. 

 The lower ligature lies close to the bull-dog (Fig. 91). 

 Place the scissors ready to cut the artery about half in 

 two at a point just below the upper ligature. (Why here?) 

 The assistant holds a piece of cotton just over the end of 

 the scissors to catch any blood that may fly out of the seg- 

 ment of artery as the operator cuts with the scissors (Fig. 

 91). With the large sharp-pointed forceps the operator 

 now holds open the artery while the assistant pushes in 

 the arterial cannula (Fig. 92) which is already connected 

 with the manometer. The washout tube and clip are also 

 on the side tube of the cannula. There is no fluid in the 

 cannula or tube connecting it to lite manometer. This fluid 

 is run in later when the operation at the neck is complete. 

 If the tip of the cannula does not enter the artery readily 

 the cannula should be dipped into a beaker of water and 

 then inserted into the artery. This is the usual method to 



