PRACTICAL EXERCISES 



55 



1*2 per cent, solution of sodium fluoride in o'g per cent, salt solution. 

 If the dog provided is a large one, these quantities may be all 

 doubled ; for a small dog they may be all halved. 



(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, f3, 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 in a cool place, and observe 

 next day that some 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 o'g per cent, salt solution. 

 Put a cannula into the centrnl end of a crural vein (p. 200). 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 lowering of blood-pressure (p. 201). As soon as the 



* 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. 186. 



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



