TEXT-BOOK OF BACTERIOLOGY. 291 



out difliculty with watery color-solutionSj but they belong to those 

 bacteria which readily fade again under the influence of bleaching 

 agents, and the staining of sections requires especial care. We 

 have already mentioned that within the rods during staining fre- 

 quently bright gaps (small unstained spots) will appear, and the 

 significance of this occurrence has likewise been discussed. 



Double staining has been so far unsuccessful with the typhus 

 bacilli; they lose their color again by Gram's method. 



Gaffky first succeeded in cultivating these bacilli artificially on 

 our ordinary media outside the body. There are developed on the 

 gelatin plate in the usual time at room temperature small white, 

 dot-shaped and superficial colonies lying deep, wide-spread, faintly 

 gray, of a peculiar lustre and irregularly bordered. Even with the 

 naked eye they remind one of the colonies of the Neapolitan bacil- 

 lus, and this similarity appears, perhaps, more distinctly under the 

 i^icroscope. The deeper ones are remarkable as slightly -granu- 

 lated, sharply-defined, yellowish-brown heaps of whetstone shape, 

 while the superficial ones appear as thin, almost completely trans- 

 parent membranes of a yellow color in the centre, but fa,ding toward 

 the borders and exhibiting the undulating, leaf-like design, the 

 linear net, noticed in the Neapolitan bacillus ; their margin is un- 

 even and serrated. The typhus bacillus (like Emmerich's) does not 

 liquefy the gelatin. 



In the test-tube culture there is an ample development along 

 the whole inoculating puncture, especially at the surface of the 

 gelatin. A thin and delicate membrane of a bluish-gray, mother- 

 of-pearl-like lustre spreads to the walls of the tube. 



This pronounced superficial growth can be excellentlj'^ observed 

 especially on oblique gelatin ; there arises on both sides of the in- 

 oculating line an almost transparent, glossy film of bluish-white 

 color. The gelatin is not liquefied, but there frequently occurs the 

 milky cloudiness in the neighborhood of the culture which is also 

 met with in the Neapolitan bacillus and traceable to the same 

 cause. The typhus bacillus belongs (as Petruschky has clearly es- 

 tablished) to the acid producers among the micro-organisms. 



On agar-agar and likewise on solid blood-serum there is de- 

 veloped a moist, white covering which has nothing characteristic 

 about it. 



It is, therefore, not so very easy to distinguish the tj'phus bacil- 

 lus, in culture, from similarly-growing bacteria, such as Emmerich's 

 faeces bacillus and many putrefactive bacteria occurring in water 

 or in the soil. The action of the typhus rods on the potato offers, 

 indeed, a secure means for a correct differentiation, since the de- 



