INTRODUCTION. 



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inject the animal after it has been killed by bleeding. The animal or part to be injected must 

 be kept warm by immersing it in water at 40 C. Even when a watery injection is employed, 

 it is as well to warm it to 40 C., as while hot it causes less spasm of the small arteries than a 

 cold mass. 



The art of injecting can only be acquired by practice. The part to be injected and the 

 mass must be at the proper temperature, no air must be allowed to enter the blood-vessels, 

 and the mass itself must not contain any particles which will block up the capillaries. One o) 

 the great difficulties is to keep the pressure constant ; this may in part be arrived at by fix- 

 ing a tube at right angles to the side of the stopcock-piece, and bringing in connection with it. 

 by means of a caoutchouc tube, an ordinary mercurial manometer, viz., a bent tube filled with 

 mercury. A pressure of two to five inches of mercury is usually sufficient for injecting small 

 animals. 



In selecting a syringe see that you get one that is capable of holding from three to six 

 ounces. The barrel ought to be long six or seven inches. For corrosive (or metallic) sub- 

 stances, a glass or vulcanite syringe must be employed. 



INJECTING APPARATUS FOR OBTAINING A CONSTANT PRESSURE. 



Ludwig was the first to introduce this arrangement. Sufficient pressure may be obtained 

 either by means of a column of mercury or a column of water. 



Fig. 24. LUDVVIG'S MERCURY PRESSURE-APPARATUS. 



a, Reservoir bottle for mercury ; b, Pressure bottle in'o which the mercury of a flows ; c, Bottle containing tlie 

 injection-mass, connected with b by one india-rubber tube, and by another with the cannula /, and by a 

 glass tube with a small manometer ; d. Handle of screw for raising the wooden shelf on which a rests ; t, 

 A screw clip, and g, a spring clip. 



Ludwig's Mercury Pressure-apparatus (fig. 24). The apparatus consists of two Wolff's 

 bottles, one of which, a, contains a reserve of mercury, and b, into which, owing to the bottles 

 being at different levels, the mercury flows. This compresses the air in b, and so acts on the 



