CLASSIFICATION 765 



seems more probable that the lactobacilli, on account of their greater acid pro- 

 duction and their ability to grow at a low pH, are implicated. Kligler (1915) 

 and Snyder (1939) noted the increased numbers of L. acidophilus in the mouths 

 of people with caries. Mcintosh, James and Lazarus-Barlow (1922, 1924) isolated 

 two varieties of lactobacilli from carious teeth, which they named L. odontolyticus 

 I and //. In glucose broth cultures these organisms produced a final pH of 2-2 

 to 34 ; and it was found that teeth left in these cultures gradually became decalci- 

 fied, the change being evident in 7 weeks. There is evidence to suggest that 

 refined sugar in the diet is a more potent predisposing factor to caries than other 

 forms of carbohydrate, but the exact mechanism by which it acts is still unknown. 

 The effect of the acid is limited, of course, by the structural integrity and 

 proper calcification of the enamel, which in their turn depend on nutritional factors 

 (see McCollum 1941). 



The repeated inoculation intravenously of very large doses of lactobacilli into 

 rabbits is said to be followed by the development of joint lesions. A mucopuru- 

 lent exudate is found in the joints, and cultures can be obtained for a week after 

 the last inoculation (Howitt and van Meter 1930). It is doubtful, however, whether 

 the organisms actually multiply within the tissues under these conditions. 



Classification 



Classification is at present unsatisfactory, partly because of some difference 

 of opinion as to which organisms should be included in the Lactobacillus group, 

 and partly by the absence of suitable criteria to serve as a basis of sub-division. 

 There seems to us good reason for including the Gram-positive members of the 

 non-sporing anaerobic bacilli isolated by Eggerth and Gagnon (1933) from the 

 human intestine in the Lactobacillus rather than in the Bacteroides group, and in 

 this we are supported by King and Eettger (1942). When we look for differential 

 characters for use in classification we are in serious difficulties. Morphological 

 and colonial appearances vary considerably, and metabolic properties and fermenta- 

 tion reactions tend to show continuous, as opposed to discontinuous, variation ; 

 so that it is difficult to do more than select modal points around which strains 

 can be grouped. Whether it is justifiable to assign specific rank to these type 

 organisms is doubtful, but provided not too many types are recognized, and pro- 

 vided it is realized that many of them are tentative, convenience alone affords 

 a strong plea for their characterization by name. 



The most serious attempt to classify the lactobacilli is undoubtedly that made 

 by Curran, Rogers, and Whittier (1933). As the result of a very careful study, 

 particularly of their metabolic characteristics, these workers were able to divide 

 103 strains of varied origin into three groups. Group A strains produced inactive 

 lactic acid, i.e., equal quantities of dextro- and Isevo-acid, from whey, failed to grow 

 above 43°-46° C. or as low as 20° C, fermented raffinose but not mannitol, and on 

 agar plates formed either the fuzzy (X) type of colony, or a mixture of fuzzy and 

 compact (Y) types. As a rule they gave rise to more CO 2 and a larger proportion 

 of volatile to fixed acids, and grew in higher concentrations of phenol and indole 

 (see Kulp 1929), than the members of the second group. Group B strains produced 

 an excess of dextro-lactic acid, grew as high as 43°-50° C. and as low as 10°-15° C, 

 fermented mannitol but not raffinose, and formed either the compact (Y) type of 

 colony, or a mixture of compact and fuzzy (X) types. They were less active than 



