700 



INFECTION AND IMMUNITY. 



Fixed 



Distribution 



virulence is retained for months (Eoux). On the 

 other hand, glycerin appears to destroy the viru- 

 lence of filtrates (Di Vestea). 



Pasteur gave the name of street v : ^us (viru* 

 virus, de rue) to that obtained from the nervous tissue of 

 dogs in which the disease develops spontaneously. 

 When the street virus is injected subdurally into 

 the rabbit the latter develops hydrophobia only 

 after an incubation period of from two to three 

 weeks. If, however, this virus is passed from one 

 rabbit to another, its virulence gradually increases 

 until the incubation period decreases to six days. 



At this point it is called fixed virus (virus fixe). 

 and its virulence can not be further increased. 

 Passage through the cat, fox and wolf also in- 

 creases virulence. On the other hand, by passing 

 it repeatedly through the monkey (Pasteur), the 

 chicken (Kraus) or the dog it becomes attenuated 

 for the rabbit and virulence may be lost entirely. 



Although virus fixe represents its highest degree 

 of virulence for rabbits, there is good reason for 

 believing that repeated passage through the rab- 

 bit decreases the virulence of the virus for man. 

 In other words, street virus is more infectious for 

 man than fixed virus. This may to some extent ac- 

 count for the success of the Pasteur treatment. 

 Ferran, indeed, uses unaltered virus fixe for the 

 protective inoculation of man. 



By means of inoculation experiments the virus 

 may be demonstrated invariably in the brain, 

 spinal cord, and usually in the salivary glands and 

 saliva of animals which have died of the disease. 

 These tissues are specifically affected, and the virus 

 probably proliferates in them. By one or another 

 observer its presence in the following organs and 



vim- 



