286 TEXT-BOOK OF BACTERIOLOGY. 



On the gelatin plate the bacillus assumes a characteristic ap- 

 pearance in a short time. The colonies appear to the naked eye 

 first as small white dots in the depth of the gelatin. But they 

 soon advance to the surface and spread there as thin yellowish- 

 white aggregations, shining like mother-of-pearl, being irregularly 

 lobulated, without ever liquefying the gelatin. 



When examined under the microscope, the smaller, deeper col- 

 onies present peculiar, whetstone-shaped structures of a dark 

 brown color and usuallj' characterized by a concentric stratifica- 

 tion of their contents. The large, superficial colonies, however, 

 appear as thin membranes of a faint yellowish color in the middle, 

 but fading toward the margin, which recede unevenly or are ser- 

 rated, and always allow a kind of mesh of lines to shine through 

 as a regular, neat leaf-like design. 



A strong tendency to superficial growth is perceived in punc- 

 ture culture. Although a rather quick development takes place 

 along the whole extent of the inoculating puncture to its extreme 

 end, the culture thrives by far most luxuriantly on the free surface 

 of the gelatin. A dry membrane, of a grayish- white lustre with 

 lobulated edges frequently breaking apart into single pieces, forms 

 on this surface. Although a liquefaction of the gelatin does not oc- 

 cur, we can (most distinctly on o'blique gelatin, but also in puncture 

 culture, and even on somewhat older XJlates) observe a milky tur- 

 bidity of the transparent medium in the vicinity of the bacterial 

 growth, frequently accompanied by a formation of rosette-shaped 

 salt crystals. Both circumstances are connected with a change in 

 the reaction of the gelatin. The Neapolitan bacillus possesses the 

 ability of neutralizing the existing alkalinity of the gelatin, produc- 

 ing an acid reaction. This can be demonstrated by adding litmus 

 tincture to the gelatin before its inoculation. The blue color will 

 soon disappear and a more or less reddish tint will take its place. 



Emmerich's bacillus grows on agar-agar as a whitish, moist 

 covering without peculiarities. 



It forms on the surface of the potato a yellowish-brown smeary 

 film of quite characteristic appearance. 



Emmerich succeeded, as stated above, in demonstrating patho- 

 genic properties in his bacillus and in producing in Guinea-pigs 

 symptoms said to agree wholly with the picture of genuine cholera. 



Weisser has subjected Emmerich's statements to a careful and 

 comprehensive examination, and reached results strikingly contra- 

 dicting Emmerich's assertions. He could not at all regularly cause 

 the death of animals by the Neapolitan bacillus, as Emmerich did. 

 He used, like the latter, various modes of infection, by inoculating 



