BY DR. BURDON-SANDERSON. 243 



The connector adapted to the canula must be of sufficient 

 length to reach an absolutely clean flask or capsule destined 

 for the reception of the blood. If serum is required, the cap- 

 sule must be allowed to stand in a cool place until it is coagu- 

 lated. If defibrinated blood, the flask must be agitated brisk- 

 ly immediately after it is collected. The blood should be taken 

 in successive portions, for in this way a much larger quantity 

 is obtained than would be yielded if the animal were allowed 

 to bleed to death at once. 



2. The apparatus for injection consists of a funnel, supported 

 on a holder at a height of about two feet from the table, to 

 the stem of which a flexible tube, guarded by a clip, is adapt- 

 ed. In addition to this, two canulae must be prepared, one 

 for the bulbus arteriosus, the other for the vena cava inferior. 

 Both should be made of thin fusible glass, and of the size and 

 form shown in figure 218. The arterial canula must be con- 

 nected by an India-rubber tube of- the same width as itself 

 with a glass joiner, and its end must be supported by a holder 

 which can be best made of a strip of sheet lead bent to the 

 proper form. The funnel having been filled with the liquid 

 to be injected, and connected with the canula by the joiner, a 

 sufficient quantity is allowed to flow into the tube to occupy 

 it completely, and the clip closed. All being now ready, a 

 frog, previously slightly curarized, is fixed on the table in the 

 supine position. The integument is divided over the sternum 

 in the middle line, and the anterior wall of the upper part of 

 the visceral cavity removed, so as to expose the pericardium, 

 great care being taken not to injure the abdominal vein, or 

 any other large vessel. The ventricle is then opened, and the 

 canula passed through the opening into the bulb, and secured 

 by a ligature. This done, the heart is drawn upwards, and to 

 the right (after severance of the small vein which stretches 

 from the back of the ventricle to the pericardium), so as to 

 expose the sinus venosus, which is then opened in the line of 

 junction between it and the auricles. By this opening, the 

 canula for the vena cava is easily introduced into the funnel- 

 shaped dilatation (see fig. 228 6), and pushed into the vein. 

 If the canula is of proper size, a ligature is unnecessary. On 

 opening the clip on the tube leading from the funnel, the cir- 

 culation is restored. The blood contained in the vascular 

 system of the animal is soon replaced by the liquid injected. 



The most instructive observations, relating to frogs in 

 which the circulation is maintained artificially (sometimes 

 called salt or serum frogs, according to the liquid used), are 

 made with the aid of the microscope. The examination of the 

 web shows us that even when saline solution is used, the ves- 

 sels and the circulation through them remain unaltered for 

 some time. If serum is used, this period is longer, provided 



