Genus: Microbacterium lAhhi. .1//)/;).) 



Of the other GRAM-positive, rod-shaped lactic acid bacteria (Table XXXII) which 

 we have encountered in our investigations, the, majority (Xos. 3 — 10) are considerably 

 smaller than the rod forms hitherto described, and have so many peculiar qualities in 

 common that it will be only natural to collect them in a genus, which may suitably be 

 named Microbacterium. 



The microbacteria do not, for the most part, curdle milk, and are on the whole weak 

 acid formers, and produce dextro-lactic acid, with the single exception of No. 10, which 

 forms inactive lactic acid. When soWn out in high agar tubes, they grow only in the upper 

 part, and in stab cultures, they exhibit more or less pronounced surface growth. No. 7 

 even forms a highly curled surface layer. Nos. .3 — 6 on the other hand, give only surface 

 growth with favourable sources of nitrogen, and even then not always to any perceptible 

 degree. The best nitrogen source for these bacteria is casein peptone ; yeast extract, on 

 the other hand, is as a rule very unfavourable. With the exception of No. 1, they split 

 up hydrogen peroxide, and reduce nitrate to nitrite. In biological respects, the micro- 

 bacteria thus greatly resemble the tetracocci, and there is also a gradual transition to 

 forms which are no longer acid formers, but which liquefy gelatin to a slight degree, 

 and can break down amino-acids. The true microbacteria never ferment pentoses, and of 

 alcohols, at the outside a little mannite. 



The microbacteria fall again into several well distinguished species. Nos. 3, 4, 5 

 and 6, for instance, are closely allied forms, and as they very often occur in milk, we 

 will call them Microbacterium lacticum. No. 7 we will call Microbacterium mesentericum, 

 from its very characteristic surface growth, and Nos. 8 and 9, which have constantly 

 exhibited a powerful yellow surface growth, Microbacterium flavum. No. 10 probably also 

 constitutes a distinct species. 



Microbacterium lacticum can endure heating to 80° — 85°. It can therefore be obtained 

 — sometines as a pure culture — by sowing out freshly pasteurised milk. It grows ex- 

 tremely poorly at anything over 35°, and hardly under 10°. Some strains develop better 

 on AG than on SG. Some few strains produce a fairly powerful solvent effect upon casein, 

 without, however, splitting it up very deeply. Mbm. lacticum may lack the power of fer- 

 menting cane sugar; it never ferments raffmose and inulin, but often starch. It occurs 

 mostly in the form of single small rods, 0,3—1 fji (Nr. ô. Pl. XLIX) but can also be swollen, 

 having then a more coccus-like appearance (No. 4, PI. XLIX). When stained with methy- 



