116 BACTERIOLOGY 



formed, upon the surface of which the pigmentation takes 

 place, owing to contact with the air, and then sinks gradually 

 downwards (fig. 40). A beautiful purple-red colour develops 

 on the surface of streak-cultures on agar, but the finest 

 growth takes place upon slices of potato or wafers, on which, 

 moreover, it progresses very rapidly at the temperature of the 

 room, being less luxuriant at higher degrees of heat. The 

 bacillus liquefies serum, and soon appears on plovers' egg 

 albumen with a beautiful rose-red colour, which extends only 

 as far as the coagulated mass has become liquid. The 

 coating shows a punctiform appearance under a low power. 

 The spectrum of the pigment, which is readily soluble in 

 water, alcohol, and ether, has three absorption bands, one to- 

 wards the violet end of the spectrum at [Fraunhofer's line] 

 D, one at E, and another at F. The red colour becomes 

 brown in the .air, owing to the action of ammonia, but 

 recovers its raspberry-red colour if acetic acid be applied. 



Wyssokowitsch, and quite recently E. Ullmann, have 

 proved that dead cultures of this bacillus are capable of 

 exciting suppuration, and Grawitz and De Bary found that 

 its pathogenesis is connected with the pigment. 



Potato bacillus. Three varieties are distinguished: Bacil- 

 lus mesentericus fuscus (Fliigge), Bacillus mesentericus ruber 

 (Globig), and Bacillus mesentericus vulgatus. They show 

 short filaments which are often connected together into 

 chains, and have the power of active movement. They 

 liquefy gelatine very quickly during their growth, whether 

 on the plate or in thrust-cultures, and form round colonies 

 which soon become yellowish, and in the case of the brown 

 bacillus (Bacillus mesentericus fitscns) assume a dark brown 

 colour. The liquefied gelatine, which swarms with bacilli, 

 also darkens (fig. 41). Upon discs of potato they grow 

 very luxuriantly, and soon spread from the upper to the lower 

 surface. The Bacillus mesentericus ruler shows at a higher 



