On Certain Bacteria fromx the Air of New York City. 343 



time necessary to determine a species. I have felt obliged to 

 use the action on gelatin as the primarj- character, because it has 

 been the onl}- medium in general use; but I find it necessary to 

 grow cultures at least two months before becoming certain that 

 liquefaction will not ultimately ensue. To the other media, I 

 have set the limit of twenty-eight days. All cultures were grown 

 at the room temperature, unless otherwise stated. 



In the Mircococci I have used the terms Merismopedia and 

 Sarcina in the generic form to indicate the general mode of asso- 

 ciation of the elements ; but I do not wish them to be understood 

 as of true generic value. They are, in some instances, of less 

 than specific value; but the}' are convenient terms, and I have used 

 them as such. It is to be hoped that further study will develop 

 some reliable practical morphological characters which will enable 

 us to divide the two unwieldy genera, Micrococcus and Bacillus, in 

 a satisfactory manner. The mode of association of the elements 

 is not such a character,* the opinions of Drs. Helme and Range 

 to the contrary notwithstanding. 



In several instances I have not been able to differentiate species 

 occurring in the air and presumably saprophitic, from pathogenic 

 parasites, and I am led to the conclusion that the pathogenic 

 property is not in all cases a test of specific diflTercnce, but rather 

 a varietal or racial character. The bearing of this conclusion on 

 the classification adopted in Eisenberg's " Bakteriologische Diag- 

 nostic " should be noted. 



The characters used in the table will be self-explanator}- for 



* Tlie mode of association of the elements is not a satisfactory generic char- 

 acter, because the differences between Micrococcus, Diplococcus, Merismopedia 

 and Sarcina may be due soley to dift'erences in the degree of the coherence of 

 the cells. They may also arise from actual differences in the manner of mul- 

 tiplication, it is true, as follows : 



(1) Cells dividing in only one plane, forming ^Micrococcus, Diplococcus, 

 Streptococcus, 



(2) Cells dividing in two planes, forming Micrococus, Diplococcus, Meris- 

 mopedia. 



(3) Cells dividing in three j)lanes, forming Micrococcus, Diplococcus, Meris- 

 mopedia and Sarcina. 



But this theoritical difference remains to be demonstrated, I think, be- 

 tween the last two, and it is certainly so obscure a one in practice as to warrant 

 the above remarks. At best these characters give but three genera instead 

 of five or six. Streptococcus is not included in this paper, and my species may 

 be all Sarcinffi with a greater or less tendency to break up into single cells. 



