68 ADVANCED LESSONS IN PRACTICAL PHYSIOLOGY 



it. To hold it firmly in place carry this ligature also around the free end of the 

 cannula. Connect the latter by means of a piece of large rubber tubing with the 

 ether bottle. 



In inserting a cannula in the carotid artery proceed as follows: Identify the 

 sternocleidomastoid muscle. Loosen its inner border from the neighboring tissues 

 by means of the blunt end of forceps. Retract the muscle laterally outward. In 

 the bottom of the wound will be found the carotid artery, internal jugular vein, and 

 vagus nerve. The carotid artery is easily recognized as a pulsating blood-vessel 

 of considerable size. While your assistant retracts the margins of the wound, free 

 the artery from its sheath by means of two forceps. Place a silk ligature around 

 it and tie it. Grasp the ligature between the thumb and middle finger of your left 

 hand, and allow the artery to rest upon the tip of your index-finger. Apply to it a 

 spring clip at a distance of about 2 cm. centrally to the ligature. By means of scis- 

 sors held in your right hand make a transverse incision in the artery at a distance 

 of about 2 mm. centrally to the ligature. Insert the beveled end of a straight glass 

 cannula through this opening (toward the heart), and secure it by means of a silk 

 ligature. 



In inserting a cannula in the distal end of the external jugular vein the same 

 procedure is to be followed. Make an incision along the outer margin of the sterno- 

 cleidomastoid muscle. Reflect the skin outward by separating it from the fascia 



FIG. 42. TRACHEAL CANNULA. FIG. 43. ARTERY CLAMP. 



(Harvard Apparatus Co.) 



underneath. Cut close to the skin, because this vein lies very superficial and is 

 easily compressed. It is recognized by its large caliber and dark color which sharply 

 contrasts it against its investment of fatty tissue. Isolate it for a distance of 3 or 

 4 cm., and ligate it with a silk thread. Apply a spring clip about 2 cm. distally to 

 the ligature. Incise it transversely in the manner just described and insert a can- 

 nula, securing the latter by means of a silk ligature. Since the vein collapses after 

 the incision the opening is sometimes not easily found. The spring clip may then 

 be opened momentarily to allow a few drops of blood to escape. Always use a 

 cannula of about the same caliber as that of the blood-vessel into which it is inserted. 



2. Arterial, Venous, and Asphyctic Blood. Release the spring clips 

 upon the artery and vein sufficiently to allow the cannulas to become 

 filled with blood. Observe the difference in color. Explain. Close 

 the tracheal tube for a short time until the animal shows forced respira- 

 tory movements. Release the clip upon the artery, and allow the blood 

 in this cannula to be displaced by fresh blood. What is the color of 

 the latter? Compare it with that of the venous blood previously with- 

 drawn. Explain this difference. Clean both cannulas thoroughly by 



