134 BACILLUS SUBTILIS AND ITS CONGENERS 



products on the part of the cells, then there result involution forms, that have lost 

 their reproductive faculty and must be regarded as diseased and moribund modi- 

 fications. A couple of these are shown in Fig. 6. Similar forms are also produced in 

 nutrient media containing a larger percentage of acids than usual, the hay bacillus 

 being very susceptible to these reagents. The locomotive powers, as well as the 

 form of the cells, are influenced by the method of nutrition. Thus, for example, 

 the cells grown in a i per cent, solution of asparagin at 25 C. are devoid of cilia. 



Bacillus subtilis liquefies nutrient gelatin. Streak cultures on agar-agar 

 develop into a wrinkled white pellicle. This microbe must be classified among 

 the extremely aerobic organisms, i.e. those essentially requiring the presence 

 of oxygen for their development. 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 percent, 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. VANDE- 

 VELDE (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 bacterial 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 spontaneously developed, wrinkled zoogloaa of rod- 

 shaped Schizomycetes, 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 considerable 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 more and more wrinkled and 

 convoluted, and recalls the appearance presented by the mesentery. 



The most common of all is the Bacillus mesentericus vulyatus, discovered by 



