418 MICROBIOLOGY 



the smear method of examination, resemble those of certain 

 known protozoa, notably of the rhizopoda. 



"If the 'Negri bodies' are living organisms they are the 

 cause of hydrophobia; a single variety of living organisms 

 found in such large numbers in every case of disease, and 

 only in that disease, appearing at the time the host tissue be- 

 comes infective, in regions that are infective, and increasing 

 in these infective areas with the course of the disease can be 

 no other, according to our present views, than the cause of 

 that disease." 



Morphology. The largest forms measured are about 18 /x 

 and the smallest about 0.5 /x.* They are round, oval, oblong, 

 triangular or ameboid. The latter are more numerous in the 

 fixed virus of rabbits and guinea pigs. They vary in number 

 according to the stage of the disease and to the infectivity of 

 the part. 



They are situated chiefly in the cytoplasm and along the 

 fibres in the branches of the large nerve cells of the central 

 nervous system. In parts of smears which are more broken up 

 the bodies may appear as if lying free, and it is these bodies, 

 if the pressure be not too great in smearing, that show the 

 structure best. In some cases the bodies are distinctly localized 

 in small scattered areas of the central nervous system. This 

 is shown especially well in smears. Whatever the variety or 

 species of animal infected, the bodies preserve the same gen- 

 eral characteristic structure, i. e., a hyaline-like cytoplasm with 

 an entire margin, containing one or more chromatin bodies 

 having a more or less complicated and regular arrangement. 



Their structure varies to a certain extent with their size. 

 In fixed virus, with an occasional exception, only tiny forms 

 are found. 



* Remlinger (Ann. de 1'Inst. Pasteur, Vol. XVII (1903) p. 834) 

 found that the virus of rabies would not pass through the close- 

 grained Chamberland B and F filters but that under certain condi- 

 tions it would go through the more open textured Berkefeld filter. 

 To produce the disease with the filtrate from 0.5 to 1 cc. was neces- 

 sary to be injected under the dura-mater. 



