372 GENERAL SYSTEMATIC BACTERIOLOGY 



Microbacterien. A name used by Billroth (1874, p. 16) to designate 

 a growth form of his Coccohacteria septica in which the cells are rod- 

 shaped and small. 



Microbacteries. Maggi (1886, p. 84) used this designation for his 

 third order of bacteria, with the single genus Bacterium. No de- 

 scription was given. 



Microbacterium. A form of the name Microbacterien (q.v.). It 

 is listed by Smith (1905) with the invalid bacterial genera, although 

 the writer has not been able to find an instance of its use as a generic 

 name previous to this time. Klein (1885, p. 37) uses "Bacterium 

 (Microbacterium Cohn)" as a heading. Apparently Klein has con- 

 fused this generic name with Cohn's Microbacteria q.v. 



In a strict generic sense the name was first used by Orla-Jensen 

 (1919, p. 179) in the following statement. 



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

 which we have encountered in our investigations, the majority (Nos. 3 to 10) are 

 considerable 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 pro- 

 nounced 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 nitro- 

 gen, 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 unfavorable. 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. Noa. 

 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 Microbac- 

 terium mesentericum, from its very characteristic surface growth, and Nos. 8 and 

 9, which have constantly exhibited a powerful yellow surface growth, Microbac- 

 terium favum. No. 10 probably also constitutes a distinct species. 



Later (1921, p. 272) he states: 



Microbacterium, is to be understood as merely a provisional collective name for 

 Gram-positive rods of size a little smaller than the ordinary bacteria. In biologi- 



