i 7 4 BACILLUS SUBTILIS AND ITS CONGENERS. 



Care must therefore be taken that air has admittance to the cultures. 

 In reference to this matter, a valuable observation was made by 

 LIBOBIUS (I.). If air be excluded, the reproduction of the cells 

 ceases, but the formation of a peptonising enzyme is not interrupted 

 so long as the medium contains sugar. As already remarked, this 

 microbe is extremely sensitive to acids, even the small quantity 

 present in normal beer-wort and beer and which, expressed as 

 lactic acid, amounts to only 0.09-0.12 per cent, in the former 

 case, and up to 0.2 per cent, in the latter sufficing to suppress 

 the development of the bacillus in question, so that the brewing 

 industry is exposed to no danger from this quarter. 



The decompositions effected by this microbe were first studied 

 by G. VANDEVELDE (I.) in 1884, who was, however, unable to 

 make use of pure cultures. On the other hand, such cultures were 

 used in the researches carried out by ADRIAN J. BROWN (II.), in 

 1895, which were specially directed to the decompositions sustained 

 by the various sugars under the influence of this fission fungus. 

 It oxidises dextrose to an (unspecified) acid, which is thereafter 

 entirely consumed, and a levo-rotatory volatile dissociation product, 

 of unknown nature, but exerting an exceptionally high reducing 

 power on copper solutions (such as those prepared by Fehling and 

 others). The decomposition of the total sugar supplied is effected 

 completely when the acid, by repeated neutralisations, is kept 

 down below 0.04 per cent. Saccharose undergoes a preliminary 

 inversion and is then oxidised. 



110. The Potato Bacilli. 



Before the great tenacity of life possessed by many of the bacte- 

 rial spores inhabiting the soil was recognised, it frequently happened 

 that potatoes, which had been presumably thoroughly sterilised, 

 became (when employed for streak cultures), infested with a spon- 

 taneously developed, wrinkled zoogloea of rod-shaped Scliizomycetes, 

 which, starting from the potato skin, rapidly extended over the cut 

 surface. These species, observed by different workers, are, with 

 reference to their habitat, named the "potato bacillus." This is 

 naturally a very comprehensive appellation, which has to be more 

 narrowly defined in each separate case. These uninvited guests 

 have their origin in the soil, sufficiently large quantities of which 

 remain in the depressions (known as <; eyes' ; ) in the potato; and 

 the germs adherent thereto will withstand any heating that is not 

 pushed too far. Of the species belonging to this group a consider- 

 able number is already known, and a few of them will be referred 

 to later on, e.g. in the chapter treating of " blown " cheeses. A 

 few others must, however, be briefly dealt with in this place, 

 namely, the three species of most general occurrence. These 

 possess in common the property of growing on solid media, e.g. 

 potato cuttings, to form a pellicle, the surface of which becomes 



