On Certain Bacteria from the Air of New York City. 327 



department of Botan3%* not to medicine which should rather con- 

 cern itself with the application of bacteriology to medical subjects. 

 To summarize then, the present state of bacteriology is this : 

 while some five hundred species of bacteria have been described, it 

 appears that this number is far from covering the entire flora, since 

 apparentl}^ new species are met with on every hand. This mass 

 of descriptions is rather a hindrance than a help to further work, 

 for not only are many species imperfectly described as compared 

 with others, but the general standard of specific descriptions is 

 inadequate to give characters to separate with clearness those 

 species already known. Again it is known that species vary, but 

 4o what extent is not known. These three factors, then, imper- 

 fect knowledge of the flora, incomplete descriptions and ignorance 

 of the extent of variation, tend to render identification of species 

 uncertain, and discourage workers in this field. It is hoped that 

 the present contribution may tend in some small measure to 

 mitiofate each of these evils. 



'o' 



Variation ix Bacteria. 



Some experiments were undertaken to give an idea of the range 

 of variation in a given species. The results are largely in accord- 

 ance with the very satisfactory conclusions expressed b}" Dr. A. 

 Rodet in his recent valuable treatise on variabiiit}^ of bacteria. f 

 Rodet concludes that the several forms of bacteria are generally 

 constant, but that they are to be regarded as diflerent races of 

 comparatively few species. I shall not enter into a discussion of 

 former work on variabilit}', as this has been much better done by 

 Dr. Rodet than I could hope to do within the limits of this paper. 

 I refer to his woi'k. 



The following experiments were directed principally toward the 

 point whether the variations among bacteria are generally of the 

 nature of " acquired characters," i. e., due to differences in the 

 environment as seems to have been generally assumed | or rather 



*0r Zoology, if we follow Ernst Haeckel's Systemat. Phylogenie der Pro- 

 tisten unci Pflanzen, Berlin 1894. 



t De la variabilite dans les microbes au point devue Morphologiqne et Phys- 

 iologique, par le Dr. A. Eodet ( 1894). 



t See Dr. J. G. Adami on the variability of bacteria and the development of 

 races, ^ledicle Chronicle, September, 1892. Also Dr. A. S. Packard on the in- 

 heritance of acquired characters, etc., Proc. American Academy 1895, pp. 

 343-344. 



