652 FILTERABLE VIRUSES— RICKETTSIA 
The original Pasteur treatment consisted in grinding a piece of 
dried cord 0.5 centimeter in length in 5 cc. of sterile salt solution, 
and injecting the emulsion subcutaneously, preferably on the abdo- 
men of the patient. Daily injections, using fresher and fresher cords 
were used, until finally a cord from a rabbit dead but twenty-four 
hours furnished the material for inoculation. The entire treatment 
required about three weeks, at the end of which time a very decided 
degree of immunity was induced. The incubation period of the 
naturally acquired disease is usually not less than six weeks. The 
advantage of instituting treatment at the earliest possible moment is 
obvious. Harris^ has found that desiccated cords, from which the 
water is removed in a high vacuum at a very low^ temperature, will 
retain their immunizing value very little impaired for several months. 
The dry, powdered material is w^eighed, standardized upon suitable 
animals, and kept in this form until needed. 
The mortality from rabies among those treated by the Pasteur 
method of immunization is less than 0.5 per cent; the average mor- 
tality of untreated cases is about 16 per cent. 
Modifications in the original Pasteur treatment, principally along 
the lines of injecting more virulent material, have been made from 
time to time, and the tendency at present is to administer a shorter 
treatment to mild cases (judged according to the location of the bite 
and the extent of local injury) on the one hand, and to administer 
a much more intensive treatment in the severe cases. The present 
routine followed in the Pasteur Institute of Paris is shown in the 
table'^ on page 653. 
Statistics indicate that a considerable degree of immunity is devel- 
oped by the end of the second week of the treatment. The duration 
of the immunity has not been definitely established, but it appears 
to last for several years. Exposure to extreme cold and excesses of 
various kinds, especially alcoholism, are said to be dangerous imme- 
diately after the treatment is completed ; they may reduce the acquired 
resistance to the virus to such a degree that the patient will succumb 
to a latent infection. 
The dangers attending the treatment are slight; in a moderate 
number of cases the sites of earlier injections may become inflamed 
after the treatment has been continued for ten days or two weeks, 
but this reaction is regarded as a modified i\rthus phenomenon depend- 
ing upon local sensitization. By far the most serious complication of 
the treatment is a paralysis which, in rare instances, appears during 
the progress of the treatment, or shortly afterward. This usually 
results fatally. The cause of this paralysis is not definitely known, 
but it is assumed that it is a modified form of the disease. 
1 Jour. Infec. Dis., 1913, 13, 155. 
2 Kraus and Levaditi: Handbuch der Technik und Methodik der Immunitats- 
forschung, 1908, 1, 713. 
