114 VASCULAR SYSTEM. 



over the water-bath. Forty or fifty minims of glacial acetic 

 acid are then added to another half ounce of warm gelatin solu- 

 tion, which is mixed gradually with the rest, with constant 

 agitation. Before the whole of the acid gelatin is added, the 

 mixture changes its color from bright red to dirty red. By 

 the addition of the last drops, the mass acquires the slight 

 acid reaction which is necessary to render it indiffusible in the 

 tissues. 



Silver Solution. The solution of silver used for injection 

 contains one-quarter or half per cent, of the salt. 



Apparatus and Instruments. Syringes of the ordi- 

 nary form answer well. They may be made of brass or 

 German silver. They are, however, now used only for special 

 purposes, e. g., for the injection of very small organs, and are 

 open to the objection that much practice is required in order 

 to regulate the pressure in such a way as to insure success; 

 deficient pressure rendering the injection imperfect, too much 

 producing extravasation. In general, and indeed in all cases 

 in which it is desirable that the pressure should be constant 

 throughout, the apparatus to be hereafter described must be 

 used. Camtlas. When the syringe is used, it is better to 

 employ metal canulas than glass ones. The former consist of 

 three parts (Fig. 17), viz., a collar, with two cross arms, and 

 a tubular beak. The beak is bevelled at the end, and is 

 grooved at a short distance from the bevelling. The dimen- 

 sions of the whole are accurately shown in the drawing. The 

 point must be carefully rounded. The nozzle of the syringe 

 is plugged into the collar, and is fitted with a stopcock, in 

 order to prevent the mass from returning after the injection is 

 completed. This object can also be answered by a ligature, 

 but in many cases this would be difficult from want of space. 

 Three or four such canulas with beaks of different calibres are 

 necessary. Glass Canutes should be made of the following 

 form : A tube is drawn out in such a manner that it tapers to 

 a degree which varies according to the size of the vessel into 

 which it is intended to be introduced. The end must be trun- 

 cated and smooth, and must have a constriction at a distance 

 of about three millimetres. The large end should also be a 

 little drawn out, so that an India-rubber tube can be easily 

 slipped over it, and secured. 



The various forms of apparatus for injection all depend on 

 the principle that the pressure which is required for injecting 

 is produced by the influx of water or mercury into a closed 

 vessel. The mechanical arrangements employed for this pur- 

 pose are as follow : A bottle containing water is suspended by 

 a pulley, so that it can be raised to any required height. 

 From a tubulature near the bottom a flexible tube issues, 

 which reaches to the table, and is connected with a glass tube', 



