62 VACCINE AND SERUM THERAPY 



period of six or seven days. Pasteur calls virus of 

 this degree of virulence *' virus fixe." 



Antirahic Vaccination : Pasteur's Vaccine. — Pasteur 

 discovered that by drying the spinal cords derived 

 from rabid animals for varying periods of time 

 he could prepare a series of viruses of graduated 

 strengths. Thus, if such a cord is dried for fourteen 

 days it loses all its toxic potency ; if it is submitted to 

 this process for only three to four days the viru- 

 lence is but little reduced. 



Immunity to rabies, as to other infective diseases, 

 can be induced by injecting at first minute doses of 

 the organism or toxin, and gradually increasing the 

 doses until at last quite strong virus can be used. 

 Graduation of the dose is effected by taking equal 

 quantities of nerval matter from spinal cords which 

 have been dried for varying lengths of time. The 

 actual vaccine consists of a small quantity (2 to 3 mm.) 

 of the cord of a rabbit which has been killed by in- 

 oculation with the "virus fixe." This is rubbed up 

 into an emulsion with 5 c.c. of sterile broth or salt 

 solution, and about 3 c.c. of the resulting fluid is 

 injected. A cord dried for fourteen days is the first 

 used ; on succeeding occasions emulsions of less 

 attenuated virus are used, until finally a portion of a 

 spinal cord dried only for three or four days is 

 used. 



If bites from a rabid animal occur about the head, 

 a more rapid form of vaccination should be em- 



