Hi INTRODUCTION. 



The principle to be attended to in making the mass is this : The carmine, if alkaline, 

 would diffuse through the tissues ; if acid, it would be deposited in fine granules, which 

 block up the capillaries hence the necessity for having a neutral fluid. The best guides 

 are the colour and odour of the fluid. The injected organ must be placed in equal parts of 

 methylated spirit and water, to which a few drops of acetic or hydrochloric acid (one per 

 cent.) are added, to prevent the carmine from diffusing into the tissues. 



APPARATUS EMPLOYED FOR INJECTING THE BLOOD-VESSELS. 



Injections arc made either with a syringe, or with some form of apparatus, which will give 

 a constant pressure. Whatever apparatus be employed it is necessary to insert a cannula 



into the blood-vessel by which the injection 



(i will flow, e.g. the aorta. The cannula^ may 



be made of brass, such as are ordinarily 

 supplied with a syringe, or they may be 

 | made of glass, with a short piece of india- 



rubber attached to them. The advantage 



C.z 



1 of a glass cannula is that one can see when 

 i air-bubbles are present. For the method 



of making these cannulae see fig. 23. 

 Fig. 23. CANNUL.-E FOR INJECTING. Natural Size. , . , , . . 



ihe cannula ought to have a shoulder, 



f ' c- c*, Glass Cannulre of different sizes ; a and b show the c . 



method of making a cannula : a glass tube is heated in a Over which the thread IS applied, SO that 



flame and drawn out to the size required, as at a. It is when t ; ed j t cannot s lj p out o f the vessel. 



then heated m the middle and slightly drawn, to make it ... 



thinner there. After it cools it is cut by means of a triangular Method 01 inserting a Cannula into a 



Meat/ and then each half is ground I down obliquely on a Blood . vess el. _ Expose the artery of the 



hone. I he sharp edges are got rid of by heating it in a flame 



for a few seconds. A piece of india-rubber tubing is tied to the part to be injected, clear a Small piece of 



end of each and the cannula is complete, c', A metal cannula; - . .. , . 



cl, A steel clamp for clamping a small artery (Schafer). it from the surrounding tissue, and place 



a ligature around it by means of an 



aneurism-needle, or a narrow-pointed pair of forceps. With sharp scissors make an oblique 

 slit in its wall, and insert the nozzle of the cannula, directing it towards the periphery. Tie 

 the ligature firmly over the artery, and behind the shoulder on the cannula. 



HOW TO INJECT BY MEANS OF A SYRINGE. f 



The syringe is made of brass, and is provided with several cannula;, of different sizes, and 

 a separate piece with a stopcock to connect the cannula with the syringe: Tic the cannula in 

 the vessel, as directed above, and fill it with salt solution, by means of a pipette. Fix the 

 stopcock-piece into the cannula, and fill it in the same way with salt solution. Then fill 

 the syringe with the injection-mass, taking care not to suck up any air. All air ought to be 

 expelled from the syringe by holding it vertically, nozzle uppermost, and expelling a few drops 

 of the injection-mass. The syringe ought to be filled and emptied several times before doing 

 this, to get rid of air. Insert the syringe in the stopcock-piece, and proceed slowly with the 

 injection. The piston must be rotated very slowly ; so that the mass is driven on slowly and 

 steadily. Half-an-hour is not too long for the injection of a rabbit. One judges of the com- 

 pleteness of the injection by observing the colouration of such vascular parts as the tongue, 

 lips, toes, or ear. After the injection is completed, turn the stopcock to prevent the escape of 

 fluid, remove the syringe, and place the part injected in equal parts of alcohol and water, or 

 any of the other fluids described at p. xxxii. If a gelatine mass be employed, it is better to 



