262 IMPORTANT VARIETIES OF FISSION- FUNGI. 



ature. This is especially marked in the Bacterium Pas- 

 teurianum, according to Hansen. 



At temperatures below the optimum of 34°, beautiful 

 chains of short rods are formed; at higher temperatures 

 the short links grow out into long undivided threads. The 

 latter, when again brought to a temperature of 34° or less, 

 in part break up into new short rods, and in part present 

 characteristic bulging. Also the bulging structures are 

 gradually changed, at least partly, under elongation, into 

 short rods, yet the widest parts nevertheless disintegrate. 

 According to Lafar, moreover, the swollen forms are partly 

 dependent upon the action of acid. 



During recent years an entire series of new varieties with 

 names have been added to these three old species, which 

 appear to be very difficult to differentiate. (Compare Hen- 

 neberg, C. B. L. iii, 223; iv, 14, 67, 138, and 933.) Also 

 Beijerinck (C. B. L. iv, 209) and his pupil Hoyer (C. B. L. 

 IV, 867) have made surprising new communications 

 regarding acetic acid fungi. Unfortunately, according to 

 the material accessible to us, the description of the mor- 

 phologic peculiarities leaves much to be desired. 



Beijerinck calls Hansen's Bact. aceti, Bacterium rancens 

 Beijerinck, and regards the Bact. Pasteurianum (including 

 Kiitzingianum) as a variety. Bacterium rancens is the 

 bacterium of sour beer. Here also belong Bact. acetosum 

 Henneberg and Bact. oxydans Henneberg. The true 

 rapidly forming acetic acid bacterium, which Pasteur first 

 isolated, and which Beijerinck now calls Bacterium aceti 

 Pasteur, is entirely different. Hansen, on the contrary, 

 did not know that the Thermobacterium aceti Zeitler 

 belonged here. Finally, Beijerinck distinguished a Bac- 

 terium xylinum. 



Their recognition may perhaps be accomplished by 

 means of the following key : 



(A) Vigorous growth forming a covering in a mixture of tap- water 

 100, alcohol 3, ammonium phosphate 0.05, potassium chlorid 0.01. 

 Upon beer forms very delicate coverings. Very slight growth upon 

 beer-gelatin, but very luxuriant, slimy growth upon beer gelatin 

 which contains 10 % of cane-sugar. Bacterium aceti Pasteur- 

 Beijerinck. 



(B) No growth on the above media. Upon beer a vigorous growth 

 forming a covering. 



