RABIES. 247 



the rapid blood-stains (Giemsa's or Wright's). The Negri 

 bodies will show blue on a darker blue field. 



Immunity. Pasteur succeeded in working out a method by 

 which active immunization could be accomplished. He found 

 that he could obtain a virus of nearly constant and fixed vir- 

 ulence by passing it through rabbits, and that this virulence 

 could be diminished by drying over caustic potash. He found 

 out that ordinary fresh " standard" virus virus fixe would 

 prove fatal to rabbits in six or seven days, and that this vir- 

 ulence was decreased more and more as drying progressed, 

 until, after fourteen days' drying, it was completely lost. 



He also demonstrated that by beginning wit^ a very weak 

 virus and injecting virus of gradually increasing strength, it is 

 possible to produce immunity. Briefly, the technique is as 

 follows : " Street virus" or virus obtained from " mad dogs," 

 is passed through rabbits until the incubation period is reduced 

 to one week. The virus is then potent enough to work with. 

 Rabbits are inoculated with an emulsion of the medulla ob- 

 tained from animals dead from rabies. This inoculation is 

 done, after removing a small piece of bone, intracranially. 

 The inoculation is best made at a point in the angle between 

 the sagittal and coronal sutures. As soon as the animal has 

 died of rabies (six to seven days) autopsy is aseptically per- 

 formed and the cord removed and hung by a sterile thread in 

 a bottle or cylinder containing at the bottom some pieces of 

 Potassium Hydrate C. P. A small piece of the infected me- 

 dulla is now emulsified with salt solution by means of a 

 sterile glass rod, and a fresh rabbit or two injected as before. 

 This is done in order to keep the supply up. The bottle or 

 cylinder containing the injected cord is put away in a dark 

 place at a temperature of 25 C., to be used after suitable 

 drying. The treatment in cases of rabies infection is begun 

 as soon as possible after infection. The injections are given 

 subcutaueously, beneath the skin of the abdomen usually. 

 The dose for injection is prepared by emulsifying about 1 

 c.m. of the dried cord in about 3 c.c. of 0.85 per cent, salt 

 solution. About two-thirds of this amount is injected, care 

 being taken to avoid injecting coarse sediment. The dosage, 



