THE POTATO BACILLI. 175 



more and more wrinkled and convoluted, and recalls the appearance 

 presented by the mesentery. 



The most common of all is the Bacillus mesentericus vulgatus, 

 discovered by Fliigge, a plump, actively motile rod, shown in Fig. 

 43. The colonies on potatoes are dirty white, can be drawn out 

 into threads, and develop equally well in the incubator and at 

 room temperature. This bacillus excretes several enzymes, one 

 being peptonising and producing liquefaction of the medium ; 

 another diastatic, and a third resembling 

 rennet, whereby the casein of milk is at 

 first precipitated, but is subsequently redis- 

 solved by the peptonising enzyme. It 

 forms endospores, the final stage of germi- 

 nation of which is shown at b in Fig. 43. 



Bacillus mesentericus fuscus was first FIG - 43- Potato bacillus, 

 described by FLUGGE (I.j. The cultures 5lwijMSrtifiS0i rod* 

 on agar-agar and on potatoes are initially just leaving the spore 

 yellow, but as their age increases deepen w*th 1 ciiii nd Ma|n?^^ 

 progressively into brown. It also produces (Drawn from a photo by 



. . 1-11-0 Neuhauss.) 



a peptonising enzyme, which liquefies 



nutrient gelatin. The production of spores is in this species less 



copious than in the foregoing and following kinds. 



The vegetative cells of the Bacillus mesentericus ruber, dis- 

 covered by GLOBIG (II.) are short rods, rather more slender in form 

 than those of B. m. vulgatus. Like the other two species, the 

 vegetative cells are motile and produce a peptonising enzyme. The 

 colour of the streak cultures on potatoes is at first reddish -yellow, 

 but subsequently becomes rose-red. The tenacity of life exhibited 

 by the endospores of this species was minutely examined by Globig. 

 A i per cent, solution of sublimate kills them after i^ hours' ex- 

 posure ; but they resist the action of 5 per cent, carbolic acid for 

 more than a fortnight. For their destruction by a current of steam 

 at 100 C. an exposure of 5 J to 6 hours is necessary, and they will 

 bear without injury an immersion of three-quarters of an hour in 

 high-pressure steam at 109-! 13 C. On the other hand, they 

 perish in twenty-five minutes in steam at ii3-ii6 C., in ten 

 minutes at i22-i 23 C., in two minutes at 127 C., and imme- 

 diately in steam at 130 C. 



The great difficulty of sterilising articles contaminated with 

 traces of soil is due to the great powers of resistance possessed by 

 the spores they contain of the species just described, as also of a 

 large number of their congeners, which are the hardiest of all 

 organisms. The preservation of numerous food-stuffs, milk in 

 particular, is thereby rendered more expensive, as will be sufficiently 

 demonstrated in the two next following chapters. At present, 

 attention will be drawn to a phenomenon which could not well be 

 referred to there, viz., a disease in bread (due to the potato bacilli), 

 which becomes manifest by the crumb of the loaf gradually 



