532 HILDA HEMPL HELLER 



of animals. But this type of character has not been worked out 

 for the anaerobic organisms and should evidently not be used 

 in classification until it has been investigated thoroughly. In 

 view of the fact that a large variety of anaerobes are to be found 

 in soil it is not advisable to state that anaerobes are ''often 

 parasitic." Habitat might be used conservatively as a descrip- 

 tive character. 



The formation of toxin and the pathogenicity for animals — the 

 most interesting of characters to the majority of us — cannot 

 logically find a place in the higher divisions of our group. They 

 become of more systematic value in classifying genera and 

 species, but they should always be used in connection with 

 other characters. Jensen's grouping of B. tetani and B. hotulinus 

 in the genus Botulohacillus because both produce toxin is not 

 advisable. The toxins produced by these organisms are dia- 

 metrically opposite in their effect on nerve tissue and that of 

 B. hotulinus and probably that of B. tetani are entirely adventiti- 

 ous so far as a parasitic mode of life is concerned. Other anaer- 

 obes of different affinities form toxins that produce still other 

 and different effects. 



We have seen with what ease objections may be made to 

 almost any morphological character used for the division of the 

 rods of higher metabolism, in case any physiological character 

 is allowed to enter into the classification. We have stated also 

 that some of the proposed morphological characters are not 

 sound for single species or even for a given culture of a single 

 strain. As Breed, Conn, and Baker say, the future must decide 

 what type of character, physiological or morphological, will 

 predominate in the classification of the bacteria. The two 

 systems are so often contradictory that they can never exist 

 side by side. One must always be used as the chief deciding 

 factor, the other as an auxiliary which may, at any time, give 

 precedence to the former. 



Experience with a single group may be misleading. The 

 higher plants, and even the fungi, may be satisfactorily classi- 

 fied on a purely morphological basis. At present the systematics 

 of bacteriology are so tentative that the matter must be left to 



