210 



SCIENCE. 



[N. S. Vol. XXIII. No. 580. 



permit of the development of lactic acid 

 the conditions become favorable for the 

 growth of this type of germ life. 



The complete paper appeared as Bulletin 

 No. 128 of the University of Wisconsin 

 Agricultural Experiment Station. 



Lactic Acid Bacteria: W. M. Esten, Wes- 



leyan University. 



Since the publication of the paper on 

 'Acid Organisms of Milk' in 1896 the in- 

 vestigations as -outlined in that article have 

 been continued. The extent of territory 

 then studied was only from Ohio to Maine. 

 Since then samples of milk have been re- 

 ceived from nearly every section of the 

 United States and from Canada. There is 

 probably no class of bacteria which has 

 caused so much confusion in regard to 

 names and classification as the lactic acid 

 group. Quite a number of investigators 

 have been studying the same organisms 

 under different names. 



In the results of these investigations are 

 found two distinct groups of lactic acid 

 bacteria. First, the gas-forming bacteria 

 and, second, the non-gas-forming bacteria. 



The first group is of much less importance 

 than the second. It consists of Bacilhis 

 coli commuTvis, which is not very generally 

 found in milk, and Bacterium lactis aero- 

 genes with all of its varieties. This is the 

 Bacillus acidi lactici of Hueppe and also of 

 Eekles. The only difference between B. 

 coli and B. lactis aerogenes seems to be that 

 of motility. This group is distinctly the 

 aerobic one. This group may be consid- 

 ered as a detrimental contamination to 

 milk and its products. 



The second group is the facultative an- 

 aerobic one and never produces gas in the 

 sugar media. Their function seems to be 

 principally the production of lactic acid. 

 Although there may be several species of 

 bacteria in this group, the author is of the 

 opinion that only one species of bacterium. 



with its varieties, belongs to this group or 

 division, namely. Bacterium lactis acidi, 

 using the name given to it by Leichman as 

 being the most appropriate. In the pub- 

 lication of 1896 it was called Bacillus 

 acidi lactici through an error, also made 

 by Gunther, thinking it was Hueppe 's Ba- 

 cillus acidi lactici. Names given to this 

 organism by investigators are as follows: 

 Streptococcus acidi lactici (Grotenfelt), 

 Bacillus acidi lactici (Gunther), Bacterium 

 lactis acidi (Leichman), Bacillus lactari 

 (Dinwidie), Bacillus a (Freudenrich), and 

 some others. In a former publication B. 

 lactis acidi I. and II. were supposed to be 

 recognized. As the result of later investi- 

 gations the No. II. should be discarded, 

 it probably being a devitalized or degen- 

 erate form of No. I. 



The characters of B. lactis acidi are al- 

 ways distinctive if grown on lactose-litmus- 

 gelatine as a small colony scarcely more 

 than one quarter to one half millimeter in 

 diameter. It avoids growth on the surface 

 almost entirely. Under mica plates it 

 grows more robust and produces more acid. 

 Colonies vary from dark opaque to light- 

 colored ones with dark specks or granules 

 in the central portion. Stumpy spines or 

 processes may or may not be present, a 

 character determined by the thickness and 

 amount of moisture, in the gelatine. In 

 sterile milk at 37° C. it curdles in from 

 twelve to twenty-four hours, after which 

 there is no further change. On lactose-free 

 agar it grows but slightly and lives only a 

 week or two on any kind of agar. The 

 best kind of media for its growth is milk, 

 milk-agar, lactose and dextrose bouillon. 



There is probably no organism, with the 

 exception of some soil bacteria, of more 

 benefit to mankind, when we consider that 

 milk which does not contain this organism 

 is a dangerous product if kept for any 

 length of time. Milk free from these lactic 

 bacteria is a good medium for the growth 



