METHODS OF INFECTION. 267 



or cloth, dipped in warm water, is then rubbed over this surface. This 

 usually makes the vein more prominent. A small clamp can be ap- 

 plied over the lower part of the vein to cause it to distend, but this is 

 by no means necessary. The ear is then bent over the index finger r 

 thus supporting- that portion of the vein which it is desired to enter. 

 The syringe is held almost parallel to the course of the vein. As the 

 needle enters the tissue one meets with the expected resistance, but 

 the moment it enters the vein, this resistance disappears. After a 

 very few trials, the student is able to tell whether or not the needle 

 has entered the blood-vessel. It should now be inserted into the vein 

 about a quarter of an inch, and the thumb then applied over the 

 point of entrance. The needle and ear are thus held between the 

 thumb and forefinger. Care must be taken to hold the needle par- 

 allel to the course of the vein. The liquid can now be gradually in- 

 jected, removing- first of all the clamp from the base of the ear, if 

 one has been used. 



As the liquid flows into the vein it drives the blood before it, 

 and hence, only a colorless stream will be seen. If there is any re- 

 sistance to the pressure on the piston, and, especially if a swelling- 

 forms at the point of inoculation, it is evident that the vein has been 

 missed. The needle should therefore be withdrawn, and the attempt 

 repeated a trifle lower down the vein. It is well always to make 

 the first attempt at penetrating- a vein as high up as possible. 

 When the needle is withdrawn, the place of inoculation should be 

 held a few minutes between the fingers, or a clamp should be applied 

 to prevent hemorrhage. 



When the amount of the liquid to be injected is large, 

 it is better to make the injection in that case into the jugu- 

 lar vein. This method requires a little more time, and 

 greater precaution than the preceding. For this purpose 

 the animal must be fastened down on some form of a holder 

 and anesthetized. 



The rabbit holder of Czermak is frequently employed 

 for fastening down rabbits and guinea-pigs. The Latapie 

 holder shown in Fig. 45, is admirably adapted for laboratory 

 purposes. It can be used equally well for rabbits, guinea- 

 pigs, chicken or pigeons. The flexed joint is placed over 

 the cross-piece of the clamp, and the ring is then bent over 

 till it is held by a spring catch. 



