CLASSIFICATION 15I 



it seems probable that some species that have been called by diiferent names are in reality 

 identical. It seems likely that Doderlein's bacillus, for example, is the same as L. acido- 

 philus (Heinemann and Ecker 1916, Thomas 1928), and for that reason we have not given 

 a separate description of it. Similarly, according to Schlirf (1926), Goadby's B. necro- 

 dentalis is identical with L. acidophilus. It is doubtful whether the Boas-Oppler bacillus 

 is a separate species ; it may quite well be identical with, or a variety of, L. acidophilus 

 (Heinemann and Ecker 1916). L. bulgaricus is quite possibly the same as the type species 

 L. caucasicus, of which no adequate description has ever been given (White and Avery 

 1910). Cruickshank (1925) suggests that L. exilis is the aerobic phase of L. bifidus ; 

 but from Tissier's (1900) original description this seems doubtful. Weiss and Rettger 

 (1934) were unable to detect any greater difference between strains of L. hifidus and 

 L. acidophilus than existed between the individual strains themselves, and they would 

 therefore regard L. hifidus as a variant of the species of which L. acidophilus is the central 

 type. The organisms described by Mcintosh and his colleagues as L. odontolyticus I and 

 // have received considerable study. Morishita (1929), Rosebury, Linton, and Buch- 

 .binder (1929), Howitt (1930), and Hadley, Buntmg, and Delves (1930) have failed to 

 find any clear distinction between oral and intestinal strains of L. acidophilus. Curran, 

 Rogers and Whittier (1933), on the other hand, conclude that the lactobacilli in carious 

 teeth do not aU belong to one species and are not usually of the acidophilus type. GUlespie 

 and Rettger (1938) also have noted diEFerences between the oral and the intestinal strains 

 of lactobacUU. For this reason we shall describe the odontolyticiis strains separately 

 from L. acidophilus. 



A number of lactic-acid-forming bacilli were isolated from cheese by von 

 Freudenreich and Thoni (1903), and named Bacillus casei by Orla-Jensen 

 (1904:). These organisms have not been fully described, and we do not propose 

 to deal with them further here. They are frequently found in milk (Sherman 

 and Stark 1927). Another organism, described by Pederson (1936) as Lactobacillus 

 plantarum, is widely distributed in fermenting plant and animal products. The 

 differentiation of this organism from Lactobacillus casei is not very clear. 



With regard to the nomenclature of this group, the term " acid-resisting " is 

 frequently employed, and, though correct, it is open to the objection that it may 

 cause confusion with the acid-fast bacilli. The term " acidophilic " is justifiable, 

 but is unfortunately a hybrid. Probably Kendall's (1910) term " aciduric " (able 

 to endure acid), which has the advantages of not being a hybrid, of not being 

 hyphenated, and of being technically correct, is the best one to employ. 



Workers studying this group may consult the annotated bibliography on L. acido- 

 philus drawn up by Frost and Hankinson (1931). Those interested in the chemical 

 constitution of this organism are referred to a series of papers by Crowder and 

 Anderson (1932, 1934a, b). 



While emphasizing again the impossibility of classifying these organisms satis- 

 factorily at present, we give a difierential table of some of the main species, 

 pointing out, however, that it is to be used only as a very rough indication of the 

 characteristics of these organisms, Table 49, p. 758. 



Lactobacillus acidophilus 



Synonyms. — Probably identical with Doderlein's bacillus, which is sometimes called B. 



vaginalis or B. crassus. 

 Isolation. — Isolated by Moro (19006) in 1900 from the faeces of breast-fed infants. 

 Habitat. — Found in milk ; the faeces of bottle-fed infants, and often of adults ; the faeces 



of nearly aU mammaha, and of many fish and invertebrates ; in saUva and 



carious teeth. 



