PRACTICAL EXERCISES 63 



(2) Insert a cannula into the central end of the carotid artery of a 

 dog anaesthetized with morphine* and ether, or A.C.E. mixture. f 



To put a Cannula into an Artery. Select a glass cannula of suitable 

 size, feel for the artery, make an incision in its course through the 

 skin, then isolate about an inch of it with forceps or a blunt needle, 

 carefully clearing away the fascia or connective tissue. Next pass a 

 small pair of forceps under the artery, and draw two ligatures 

 through below it. If the cannula is to be inserted into the central 

 end of the artery, tie the ligature which is farthest from the heart, 

 and cut one end short. Then between the heart and the other 

 ligature compress the artery with a small clamp (often spoken of as 

 ' bulldog ' forceps). Now lift the artery by the distal ligature, make a 

 transverse slit in it with a pair of fine scissors, insert the cannula, and 

 tie the ligature over its neck. Cut the ends of the ligature short. If 

 the cannula is to be put into the distal end of the artery, both ligatures 

 must be between the clamp and the heart, and the bulldog must be put 

 on before the first ligature (the one nearest the heart) is tied, so that 

 the piece of bloodvessel between it and the ligature may be full of 

 blood, as this facilitates the opening of the artery. 



(3) Run into a, /3, and 7 enough blood to fill them to the mark. 

 Shake the vessels, or stir up once or twice with a glass rod, to mix the 

 blood and solution. 



(4) Take a small thin copper or brass vessel, and place it in a freezing 

 mixture of ice and salt. Run into it some of the blood from the artery. 

 It soon freezes to a hard mass. Now take the vessel out of the 

 freezing mixture and allow the blood to thaw. It will be seen that it 

 remains liquid for a short time and then clots. 



(5) Run some of the blood into a porcelain capsule, stirring it 

 vigorously with a glass rod. The fibrin collects on the rod; the blood 

 is defibrinated and will no longer clot. 



(6) Now let some blood run into a small beaker or jar. Notice that 

 the blood begins to clot in a few minutes, and that soon the vessel 

 can be tilted without spilling it. Note the time required for clotting 

 to occur. Set the coagulated blood aside, and observe next day that 

 clear yellow serum has separated from the clot. 



(7) Weigh out a quantity of Witte's ' peptone ' equivalent to 

 0-5 gramme for every kilo of body-weight of the dog. Dissolve the 

 peptone in about twenty times its weight of 0-9 per cent, salt solution. 

 Put a cannula into the central end of a crural vein (p. 212). Fill the 

 cannula with the peptone solution and connect it with a burette. Put 

 15 drops of the peptone solution into a test-tube labelled ' Peptone A.' 

 Put the rest into the burette, and see that the connecting tube is filled 

 with the solution and free from air. Run into the test-tube about 

 5 c.c. of blood from the cannula in the carotid. Now let the peptone 

 solution flow from the burette into the vein. Feel the pulse over the 

 heart as the solution is running in. If the heart becomes very weak, 

 stop the injection ; otherwise the animal may die from the great lower- 

 ing of blood-pressure (p. 214). As soon as the injection is finished, 

 draw off a sample of 5 c.c. of blood into a test-tube labelled ' Pep- 

 tone B,' and let it stand. In ten minutes collect five further samples 

 of 5 c.c. (' Peptone C, D, E, F, G '), and a large one, H; in half an hour 



* One to 2 centigrammes of morphine hydrochlorate per kilogramme of 

 body-weight should be injected subcutaneously about half an hour before 

 the operation. Ten c.c. of a 2 per cent, solution is sufficient for a dog of 

 good size. Note that diarrhoea and salivation are caused by such a dose. 

 For directions for fastening the dog on the holder, see footnote on p. 199. 



t A mixture of i part of alcohol, 2 of ether, and 3 of chloroform. 



