606 THE ARTERIES. 



moment ; as it matters little whether the blood comes from one source rather 

 than another, or that a collateral vessel becomes the principal at the expense of 

 the parent trunk, provided its relations are not altered, and the principle of 

 immutability of connections is maintained. 



Preparation of the Arteries. — This requires two successive operations : 1. lujection. 

 2 Dissection. 



Injection of the arteries. — The object to be attained in injecting these vessels, is to intro- 

 duce into their interior a solidifiable substance which will cause them to assume the volume 

 and f'onformation they presented during life, when they are filled with blood. 



Tallow, coloured by lamp-black, is the most convenient and general injecting material. 

 Sometimes a solution of gelatine, with the addition of a certain quantity of plaster of Paris, is 

 used ; but this is seldom employed in the French scliools. A copper or brass syringe, and 

 a cannula witli a stop-cock to fit ou its extremity, are the only instruments necessary to propel 

 these matters into the arteries. 



The following are the details of the operation, when it is desired to make a general injec- 

 tion : — The animal being placed ou a table, the carotid artery is exposed by an incision in the 

 jugular channel, and opened longitudiually. A ligature is applied above the opening, and the 

 tube, with the stop-cock, is firmly fixed in the cavity of the artery towards the heart by 

 a second ligature. The injection, previously prepared, is taken up by the syringe, which ia 

 fitted into the tube, and the piston pushed, in order to drive the contents of the instrument 

 into the arterial canals. 



To perform the operation successfully, the following precautions are to be attended to: 

 1. Inject tlie vessels of an animal killed by effusion of blood, and yet warm. 2. If suet is 

 employed, and wiiich is always to be recommended, make it so hot that tlie finger can scarcely 

 endure it. When it is colder than this it solidifies too quickly, and when hotter it shrivels up 

 the sigmoid valves, passes into the left ventricle, and from thence into the auricle and pul- 

 monary veins — an acciilent generally attributed to the too-powerful force applied to the piston 

 of the syringe. 3. Do not make any undue pressure on the piston, though this does not strain 

 the sigmoid valves so frequently as is believed. 4. Cease injecting when the arteries react, by 

 their elasticity, on the piston, so as to drive it back in the syringe. 



In order to ensure the retention of the injected matter in the arteries, and prevent the 

 sigmoid valves being forced, a cork may be introduced into the aorta through the left ventricle, 

 and firmly tied there by a strong ligature ; the cork should have a transverse notch for the 

 reception of the li<:ature. 



Instead of injecting by the carotid, a long curved cannula may be fixed to the aorta itself, 

 after making an opening in the left side of the chest, on a level with the heart, by the ablation 

 of two segments of the ribs, and incising the pericardium and left auricle to introduce it. This 

 mode allows the tallow to be injected at a very liigh temperature, and gives the best results, 

 for it can then penetrate to the capillaries, if we only know how to manage it ; in certain organs 

 the injected matter may even be made to return by the veins. 



But no matter what procedure may be adopted, there are several parts into which the 

 tallow can never be made to enter by a general injection ; these are the four extremities. So 

 that a special operation must be resorted to, in order to fill their vessels. After separating 

 them from the trunk, by sawing them through above the knees and hocks, tliey should be 

 allowed to steep for two hours in water, constantly kept up to a temperature of from 140° to 

 160° Fahr. at most; it is then easy to inject them, either by the posterior radial artery, or the 

 anterior tibial, after tying those branches which may be open at the cut extremity of the limbs. 



If it is desired to make partial injections in other parts of tlie body, it will be better not to 

 sepaiate them from the trunk; but only to tie those vessels which anastomose between the 

 arteries to be filled and those which are not. For example, to inject the arteries of the head, 

 it suffices to push the mixture into one of the common carotids, after ligaturing the other in 

 the middle of the neck, and both vertebrals in the space between the two portions of the 

 scalenus muscle. 



We may give the tallow more fluidity, and a higher degree of penetration, by mixing with 

 it a little spirits of turpentine ; or more consistence, in adding to it a small proportion of 

 beeswax. 



The two following mixtures are borrowed from Oruveilhier's Anatomy : — 



Tallow 9 parts. 



Turpentine 1 part. 



Ivory Black, mixed witli spirits of turpentine . . 2 parts. 



