GENERAL CONSIDERATION OF F1LTRABLE VIRUS 911 



He tests virulence by injecting 0.1 c.c. of the dilution into 

 the brain of a rabbit, by trephining and passing a very fine hypo- 

 dermic needle through the brain to the base or into the lateral 

 ventricle, so that none of the material may escape when the needle 

 is withdrawn. He finds that, by this method, his material after 

 preservation of three weeks, is equivalent to that of fresh cord. 

 After fifty days it is 25 per cent more infective than the same quan- 

 tity of the "one day" cord of the old method. After 200 days its 

 infectivity is exactly equal to that of the "two day" cord of the 

 old method. After 500 days it is two and one-half times as infective 

 as the "three day" cord. The only precaution that is absolutely 

 essential is that in preparing and preserving the diluted material, 

 the presence of moisture must be absolutely prevented. 



Having prepared this material, Harris thought it worth while to 

 follow the suggestion of Hogyes who has developed a method of 

 immunization dependent upon the dilutions of virulent virus, in- 

 stead of using the Pasteur method of quantitative destruction by 

 drying. Hogyes had treated 10,000 patients by his method without 

 accident, giving from 70 to 220 M. I. D., or minimal infective doses 

 for rabbits, the first day and from 200 to 400 M. I. D. on the second, 

 the M. I. D. being, as in Harris's experiments, determined by injec- 

 tions into the brains of rabbits. Harris has constructed charts from 

 careful experiments in which he tabulates the proportion of infec- 

 tious to non-infectious material in a milligram of desiccated brain 

 after preservation for various periods. Unlike Harvey and Mc- 

 Kenderick (quoted from Harris) who believe that when rabic virus 

 has lost its infectiousness, it no longer has the power of conferring 

 immunity, Harris believes that when all the infectivity of rabic 

 material has been destroyed rapidly by light and various tempera- 

 tures, it still has considerable powers of conferring immunity. It is, 

 of coarse, impossible to determine the degree of immunity conferred 

 by the non-infective portions of desiccated material. 



Harris begins his treatment with material in which the proportion 

 of living to non-infective material is estimated as being about 1 to 

 25, that is, material at least six months old. As the treatment 

 continues, he gradually increases until he uses material which con- 

 tains 100 M. I. D. per milligram. In two years of such treatment, 

 he had no accidents either in patients, dogs or rabbits. 



Attempts to treat active rabies with the sera of immunized 

 animals have so far been unsuccessful. 



