710 INFECTION AND IMMUNITY. 



improved technic. In 1886 the number of deaths 

 which occurred after fifteen days had passed 

 amounted to 0.94 per cent; in 1902 to 0.18 per 

 cent. 

 immunity The immunity established by the Pasteur treat- 



and Serum ... . ,,,,.,., 



Properties, ment is, in all probability, antimicrobic in nature. 

 The serum of both man and animals, after immun- 

 ization, is able to destroy the infectiousness of rabic 

 nervous tissue, i. e., the serum is rabicidal (Babes 

 and Lepp, 1889). The technic of Kraus and 

 his co-laborers is well adapted to show the rabi- 

 cidal properties of the immune serum. Eabid ner- 

 vous tissue is made into an emulsion with salt 

 solution in a dilution of 1 to 100, and then filtered 

 through paper to remove coarse particles of tissue. 

 To quantities of 0.5 to 1.0 c.c. of this emulsion 

 varying amounts of fresh immune serum are added, 

 and after eighteen hours' contact the mixtures are 

 injected into rabbits to determine the degree of 

 infectiousness. Small quantities of rabicidal sub- 

 stance may be detected in this way. 



Natural resistance to hydrophobia does not go 

 hand in hand with the antirabic power of an ani- 

 mal's serum. Old pigeons, for example, develop the 

 disease following intracerebral injection of the 

 virus, although their serum is not rabicidal. 



Babes and Lepp also showed that the immune 

 serum has protective powers which are analogous 

 in their efficiency with those of bactericidal serums. 

 Babes advocates and practices the mixed method 

 of immunization in severe cases, immune serum be- 

 ing injected in addition to the virus. The serum 

 has little or no curative value. 



