words, the use of Bacillus for spore-forming rods at a later period cannot be properly inter- preted as rendering generic names of non-spore-forming rods with the suffix -bacillus ille- gitimate. Stability in bacteriological nomenclature can, it is believed, be best brought about by observing the rules of the internationally accepted Bacteriological Code. Under this Code no one has authority to reject, change or modify a name because in his judgment another name is preferable. Exceptions to rules should be internationally approved. The type species is Lactobacillus caucasicus Beijerinck. It is impossible to make an entirely satisfactory differentiation of the species in the genus Lactobacillus due to the inadequacy of comparative data. The end-products of fermenta- tion, utilization of carbon compounds and temperatures of growth are the criteria relied upon at present. It is quite possible that when more comparative information is made avail- able in regard to nutritional patterns in defined media, serological reactions and variations in sugar fermentations, a more satisfactory arrangement of species may be effected. See Rogosa, Wiseman, Mitchell, Disraely and Beaman (Jour. Bact., 65, 1953, 681), Tittsler, Geib and Rogosa (Jour. Bact., 54, 1947, 12), Williams (Jour. Inf. Dis., 82, 1948, 31) and Or- land (Jour. Inf. Dis., 86, 1950, 63). Key to the, species of genus Lactobacillus. I. Homofermentative, producing only traces of end-products other than lactic acid from glucose. Sub-genus Lactobacillus Beijerinck (Arch, n^erl. d. sci. exact, et nat., Hadr- lem, Ser. 2, 7, 1901, 212). A. Optimum temperature, between 37° and 60° C. or higher. 1. Produce acid from lactose. a. Optimum temperature, between 37° and 45° C. b. Produce levo rotatory lactic acid. 1. Lactobacillus caucasicus. 2. Lactobacillus lactis. bb. Produce optically inactive or dextro rotatory lactic acid, c. Microaerophilic. 3. Lactobacillus helveticus. 4. Lactobacillus acidophilus. cc. Anaerobic in freshly isolated cultures. 5. Lactobacillus bifidus. aa. Optimum temperature, between 45° and 62° C; usually no acid from maltose. 6. Lactobacillus bulgaricus. 7. Lactobacillus thermophilus. 2. Does not produce acid from lactose. 8. Lactobacillus delbrueckii. B. Optimum temperature, between 28° and 32° C. 1. Produce optically active lactic acid. a. Produces dextro rotatory lactic acid. Often prefers lactose to sucrose and maltose. 9. Lactobacillus casei. aa. Produces levo rotatory lactic acid. 10. Lactobacillus leichmannii . 2. Produces optically inactive lactic acid. 11. Lactobacillus plantarum. II. Heterofermentative, producing considerable amounts of end-products other than lactic acid from glucose (carbon dioxide, alcohol and acetic acid; mannitol from fructose). Sub-genus Saccharobacillus van Laer (Contributions a I'Histoire des Ferments des Hy- drates de Carbone. Mem. Acad. Royale de Belgique, 47, 1892, 5). A. Optimum temperature, between 28° and 32° C. Usually ferment arabinose.
