THE PATHOGENIC RHIZOPODA 305 



repeatedly inoculated in animals of the same kind, and, owing to their 

 very minute size, such organisms are easily overlooked in this "fixed" 

 virus. It has been found by Remlinger, Schiider, Bertarelli, and 

 others that the virus is still effective after filtration through a Berkefeld 

 filter, a fact used as an argument against the specific pathogenicity of 

 these structures ; but the well-known variations in size of ameboid 

 protozoa and the small size of some stages of the organism, combined 

 with plasticity, which suggests ameboid movements, explains the 

 ability to pass a filter. Other protozoa, notably spirocheta and 

 trypanosoma, likewise pass through the Berkefeld. It is probable, 

 therefore, that an organism as variable as neuroryctes in size would 

 have some stages minute enough to escape filtration. 



Negri was the first to make out the typical nucleus of the organism 

 and to call attention to the distributed granules, although he didjiot 



FIG. 120 



Form and size changes of the organism of rabies, with evidence of budding in 

 some cases. (After Williams and Lowden.) 



interpret these correctly, Williams and Lowden, in 1906, being the 

 first to interpret them as granules of distributed chromatin. Negri, 

 in 1905, found that the nucleus has either a solid or reticular structure, 

 according to the success in staining (Fig. 119), while the cell body 

 contains a variable number of chromatin granules. 



Reproduction of Neuroryctes hydrophobia, according to Williams 

 and Lowden, occurs by simple division and by budding. The division 

 is either an equal binary fission, in which nucleus and chromatoid 

 material are distributed to the two cells, although nothing like mitosis 

 was observed. In budding, small buds are pinched off, these buds 

 being single or multiple in number and containing granules of chro- 

 matin. The possibility of conjugation was suggested by Williams and 

 Lowden, and illustrated by figures, but it is equally possible, and more 

 probable, that the cases cited and illustrated were cells in division. 

 Finally, what appears to be a spore-containing cyst (Fig. 120) was also 

 described. 

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