184 ACTIVE IMMUNIZATION 



on successive days with material of increasing virulence, beginning 

 with that which is altogether innocuous, i. e., twelve to fourteen 

 days old. 



The technique employed in the preparation of the virus and the 

 immunization of the patient, as described below, is that in use at 

 the Pasteur Institute of the College of Physicians and Surgeons of 

 Baltimore, under the direction of Dr. N. G. Keirle, and represents 

 the original Pasteur method. 



Preparation of the Virus. The original virus was obtained from the 

 Pasteur Institute of Paris, and had been started from the medulla 

 of a rabid cow in 1882. It has since been transferred from rabbit 

 to rabbit, and has now reached about the nine hundredth remove. 

 Another virus was started by Dr. Keirle himself from the medulla 

 of a rabid cow, and has reached about the six hundredth remove. 

 As a rabbit will live about twelve days after inoculation, about 

 thirty passages may be made in a year. 



The inoculations are made as follows: "The hair between a line 

 drawn transversely through the ears and eyes is cut off with scissors 

 and washed with a 3 per cent, solution of carbolic acid. No anesthetic 

 is required; the animal does not cry out, and evinces no sign of pain. 

 The animal need not be strapped down, but may be held on the table 

 by an assistant. A cut one inch and a quarter long is made with 

 the knife or scissors, longitudinally, through the skin in the middle 

 of the space at the top of the head between the lines above named. 

 A blepharostat keeps the incision apart, and the sublying tissue is 

 scraped away so as to expose the bone a little to one side of the median 

 line. The trephine has a diameter of 5 mm. and a ring guard which 

 is set at 2 mm. from the cutting end of the crown; the trephine may 

 be a bit fastened in a revolving drill handle, or a simple hand trephine 

 made of metal rod 17 cm. long. The button of bone is removed with 

 a tenaculum and the dura is exposed, and an ordinary hypodermic 

 syringe is used to inject three or four drops of the rabic emulsion 

 beneath the dura. If the perforating end of the needle is curved 

 almost at a right angle for a space of 4 mm. it facilitates its introduc- 

 tion, but this is by no means indispensable. The wound is closed 

 by interrupted sutures (three are generally sufficient) and then sealed 

 with collodion. The ordinary suture needle can be used, but the risk 

 of sticking the hand is lessened if the needle has a fixed handle, 

 the other extremity terminating in a spear with a slit in its side, 



