384 BACTERIA IN MILK 



lactis Beijerinck, 1901, p. 213; Streptococcus giinthcri Lehmann and Neumann, 1904, p. 242; 

 Bacillus lactis acidi Sewerin, 1908, p. 8 (Not Bacillus lactis acidi Marpmann, 1886, p. 120, nor 

 Leichmann, 1896, p. 778); Bacterium Icichmanni Wolff, 1909, p. 57. 



This long list of synonyms is due to the complicated but interesting history of this im- 

 portant milk organism. It is a history that is intimately interwoven with the develop- 

 ment of bacteriology as a science. 



Pasteur' in 1857 was the first to get a clear conception of the processes involved in 

 the fermentation of sugars by micro-organisms with the production of lactic acid. He 

 had previously brought about a popular revival of Schwann's theory that alcoholic 

 fermentation was due to living organisms, the yeasts. Because of this, he began his 

 lactic-fermentation studies confident that this fermentation also was caused by micro- 

 organisms. Soon he found it to be caused by minute, non-motile organisms, which, 

 because they were non-motile, he regarded as yeasts rather than vibrios. 



While he worked with milk fermentations in part, he did more work with sugar 

 bouillons, and reports that in some cases the products of fermentation were CO2, H2, 

 and butyric as well as lactic acid. Thereby he showed that he probably had an organ- 

 ism of the colon group, mixed cultures, or at least that he did not have the organism 

 causing the normal souring of milk. 



Hoffmann^ was the first to apply the term "bacteria" to these lactic ferments and 

 to insist that these forms were more closely related to Pasteur's "vibrion butyrique" 

 than to yeasts. The first worker whose descriptions show clearly that he was dealing 

 with the sour-milk organism was Lister.^ His work in this field was done between 1872 

 and 1878. In the second of a series of papers that he prepared and the first published, 

 he gives a detailed report of his experiments with the lactic fermentation of milk. In 

 this he describes the microscopic appearance of the sour-milk organism and proposes 

 the name Bacterium lactis for it. His attempts to cultivate the organism in Pasteur's 

 solution, urine, and the like resulted in his mistaking contaminating organisms for the 

 sour-milk bacterium. This being in a period before satisfactory pure-culture methods 

 had been developed, and a time when contaminations were popularly regarded as 

 pleomorphic stages in the life of the organism. Lister naturally fell into this error. 

 He was too keen an observer to be misled long, and in his subsequent experiments 

 succeeded in isolating pure cultures by means of the dilution technique. He did this 

 by making a microscopical estimate of the number of bacteria in a small drop of sour 

 milk, and then diluting it with enough sterile water to make the number of bacteria 

 less than four per drop. Drops were then added to tubes of sterile milk whereupon one 

 out of five tubes inoculated with the most highly diluted milk soured normally with a 

 smooth curd while the remaining four showed no change, and no bacteria by micro- 

 scopical examination. 



Thus Lister secured a pure culture of his Bacterium lactis at the period when 

 Schroeter^ was securing cultures of chromogenic bacteria by exposing pieces of cooked 



' Pasteur, L.: Compt. raid. Acad, de sc, Paris, 45, 913. 1857; Ann. dc chem. ct phys. (3d ser.), 52, 



404. 



2 Hoffmann, H.: Bot. Ztschr., Nos. 15-20. 1869. 



3 Lister J.: Quart. J. Micr. Sc, 13, 380. 1873; ibid., i8, 177. 1878. 

 ^Schroeter, J.: Beilrdge z. Biol. d. Pflanzen, i, Heft 2, 109. 1872. 



