12 



which thereby simultaneously develop; it is, however, a good way to get an initial 

 material for the said accumulations themselves. 



It seems to us that the generaUty of B. polymyxa in our surroundings and par- 

 ticularly in the soil should be explained by lts pectinase secretion, which must give 

 this species, in combination with its Httle want of air, a great advantage over the 

 other saprophytes. 



The very common presence of B. polymyxa in the bark of the nodules of the Le- 

 guminosae is certainly also a direct consequence of its pectinase production. lts pre- 

 sence there is of so general occurrence, that it reminds more of symbiosis than of 

 saprophytism. In the bacteroïdal tissue B. polymyxa is however completely absent. 



Properties of the colonies. 



The colonies on agar as well as those on gelatin are characteristic. On malt-wort 

 gelatin they resemble at first thin, watery, sideways quickly extending, slowly h- 

 quefying layers, which by and by become deeper and cloudy by their strong growth. 

 At length the gelatin is completely liquefied and then these cultures resemble those 

 of common hay bacteria. On malt-wort agar there is a profuse production of slime, 

 whence very distinct voluminous and wrinkled colonies appear. The slime attracts 

 part of the pigment from the wort-agar thereby becoming brown-coloured, which 

 gives a characteristic appearance to the colonies. 



On glucose-kalium-phosphate-ammonium-phosphate-agar they become glass- 

 like transparent, somewhat resembling glass globules, so peculiar that at estimating 

 the number of germs in soil samples, they may directly be recognised and counted. 

 Silica plates, saturated with food, also produce such drop-like colonies from soil. 

 Some varieties form much less slime than others and this slime is either tough or soft. 



Microscopically those with soft slime consist of much shorter rodlets. Hence, 

 one is at first disposed to think of different species, but further research shows the 

 similarity, which is the more convincing,' when beside the natural varieties, the muta- 

 tion phenomena in the pure cultures are studied. On cane-sugar-asparagine agar many 

 colonies, at first quite homogeneous and soft, when getting older produce small, 

 rather solid, transparent, secundary colonies which, after separation from their sur- 

 rounding (which is not easy) prove to be constant. On malt-wort agar the variety 

 with tough slime, w-hen growing older produces extensive, flat secundary colonies, 

 showing a hereditary loss of the factors for slime formation. 



In liquid nutritive media the form resistent to high concentrations of the food 

 gives remarkable cultures. 



In a malt-wort of 10° Balling at 30° they consist of excessively voluminous 

 slime masses, forming after one or two weeks a thick, coherent, floating film, inflated 

 by carbonic acid, whilst no hydrogen is detectable. Only in the anaërobic butylic 

 fermentation something of the like may be observed but then much hydrogen is 

 present. Even the most slimy Aërobacter forms produce quite different submerged 

 cultures equally dispersed through the solution. 



The vigorously fermenting slime varieties of B. polymyxa produce aceton, proba- 

 bly after the formula 



CéHnOe + 2 O2 = CiH^O -f 3 CO2 + 3 H2O. 



