123 



the 45 years which have passed since BEIJERINCK made the observa- 

 tion referred to above l ). 



It was not until 1901 that BEIJERINCK decided to make public the 

 vast experience which he had gathered during his industrial period 

 regarding the lactic acid bacteria active in the yeast and alcohol 

 industry 2 ). In this publication a survey is given of the various rod- 

 shaped lactic acid bacteria- which are frequently encountered in the 

 industry in question. BEIJERINCK laid it down that they constitute a 

 group which is homogeneous both from the morphological and from 

 the physiological point of view, and accordingly he felt justified in 

 ascribing to this group the natural rank of a genus, for which he 

 proposed the name Lactobacillus. 



For a survey of the various Lactobacillus species with which BEIJE- 

 RINCK had become acquainted in his industrial period, it may suffice 

 to refer the reader to the original paper, and to the thesis of JAN SMIT 

 which thesis about ten years later was prepared under BEIJERINCK'S 

 supervision 3 ). It seems worth-while, however, to mention here briefly 

 the various properties which BEIJERINCK considered to be character- 

 istic for true lactic acid bacteria. 



In the first place BEIJERINCK stressed the absence of hydrogen in 

 the fermentation gas, when such gas is produced. BEIJERINCK pointed 

 out that this characteristic is of significance in the differentiation of 

 the lactic acid bacteria from the bacteria belonging to the genus Aero- 

 bacter, as outlined by him 4 ), which bacteria also produce larger or 

 smaller quantities of lactic acid from sugar. There seems little doubt 

 that the criterion in question is quite valid, though it has remained 

 unnoticed by later investigators. Even in ORLA-JENSEN'S classical 

 monograph, "The Lactic Acid Bacteria", which appeared in 1919, one 

 finds the casual remark that hydrogen may occur in the fermentation 

 gas produced by true lactic acid bacteria. Since, however, no docu- 

 mentation for this contention is presented, ORLA-JENSEN'S 

 remark may be considered as a relic of the confusion which formerly 

 existed regarding the definition of "lactic acid bacteria". 



Further general characteristics of true lactic acid bacteria as sus- 

 tained by BEIJERINCK are: complete immotility in all stages of 

 development ; the small dimensions of the colonies, even under 

 favourable nutritional conditions; and the absence of catalase, as 

 already discussed above. In addition it is pointed out that peptones 

 are the only suitable nitrogen source for the lactic acid bacteria. This 



!) For an acetic acid bacterium not containing catalase, viz., Acetobacter peroxydun*. 

 cf. F. VISSER 'x HOOFT, Biochemische onderzoekingen over het geslacht Acetobacter, 

 Delft 1925, and also H. WIELAND und H.J.PisxoR, Ann. d. Chemie 522, 1 16, 1936. 



2 ) Arch, neerl. d. sciences exactes et naturelles Ser. II, 6, 212, 1901. 



3 ) JAN SMIT, Bacteriologische en chemische onderzoekingen over de melkzuur- 

 gisting. Diss. Amsterdam, 1913. 



4 ) It should be realized that nowadays the genus Aerobacter BEIJERINCK is used in a 

 much more restricted sense. As originally created by BEIJERIXCK it was meant to 

 embrace all bacteria of the so-called coli-aerogenes group. 



