116 VASCULAR SYSTEM. 



is obvious. The inequalities of the pressure, which are its 

 chief disadvantage, are annulled by the elasticity of the air 

 contained in the bottle, which serves as a kind of cushion. 

 While the operator fixes his attention on the canula, an 

 assistant gradually injects air into the bottle until the con- 

 tents of the syringe are discharged. The tube must then be 

 closed with a screw-clamp, and the operation, if necessary, 

 repeated. 



When warm masses are used, it is commonly necessary to 

 place the injection-bottle in a water-bath, kept warm by a 

 spirit lamp. It is also desirable to keep the object warm, for 

 which purpose it is placed on a plate of glass over a water- 

 bath ; or (as in Ludwig's arrangement) a warm chamber of 

 metal supported on a tripod is used, which is large enough to 

 hold both the animal and the bottle containing the injection. 

 It is furnished with a cover and air opening for the admission 

 of the compressed air. 



In order to illustrate the method more completely, I will 

 describe three injections. In the first of these examples the 

 syringe is used in the ordinar}'- way ; in the second it serves 

 as a pump for the injection of air into the Woolff's bottle con- 

 taining the mass ; in the third, the apparatus is used. Sup- 

 pose that it is desired to inject the kidneys of a small mammal 

 with cold two per cent, solution of Prussian blue. The animal 

 having been just killed by bleeding, the abdomen is opened 

 and the whole mass of intestines pushed aside to the right. 

 The left renal artery is then separated from surrounding parts 

 with the aid of two pairs of ordinary forceps without any cut- 

 ting instrument. A silk ligature is placed round the artery, 

 and looped near to the point at which it enters the kidney. 

 The vein is next prepared in the same way, and a ligature 

 placed round it close to its junction with the vena cava. By 

 drawing on the renal vein, it is easy to make a valvular open- 

 ing with fine scissors. The artery is similarly opened short 

 of the loop, and the metal canula with its stopcock intro- 

 duced, the edge of the incision being held aside with the for- 

 ceps. In making the opening and inserting the canula, the 

 greatest care must be taken to avoid rupturing the artery or 

 cutting it through with the scissors. The moment that the 

 canula is in the artery, the loop must be tightened round the 

 groove. The canula and nozzle are then filled with half per 

 cent, salt solution with the aid of a capillary tube : the syringe 

 is charged with the liquid and connected with the nozzle. In 

 injecting, the piston must be slowly pushed forwards. As 

 soon as the organ becomes blue, and the liquid appears to pass 

 unmixed from the opening in the vein, I stop, and then direct 

 my assistant to close the vein with a clip, or to tighten a loof) 

 previously placed round the vessel for this purpose. This 



