324 On Certain Bacteria froTti the Air of New York City. 



of life, the organization becomes simpler, till with the bacteria 

 we reach organisms which present extremely slight differences, 

 so slight that morpholog}' almost fails to furnish generic charac- 

 ters, and entirely fails to differentiate every species. 



If conjugation is absent among the bacteria, and has never 

 been present, the cells reproducing always by fission into equiva- 

 lent parts, a condition of affairs should exist such as assumed by 

 Weismann for the primitive form of life, and we should see all 

 characters acquired byan^' species under the influence of external 

 conditions, strictly inherited. In this case, there would be no such 

 thing as species among the bacteria, merely an indefinite number of 

 intergrading varieties. A given culture would probably show con- 

 stant characters, but it would scarcely be expected that another 

 culture would ever be found to show exactly the same characters. 



But owing to the nature of the bacteria, dependent, for the 

 most part, on previously prepared nourishment, it seems more 

 probable that the}' are degraded forms, perhaps derived from 

 ancestors in wliich the sexual process was represented. More- 

 over, the strict inheritance of acquired characters does not occur, 

 since modified species ma}- return to their original characters. 

 Further, it is scarcely' possible to eliminate the eff"ects of selective 

 action, which maj' be the true agent in producing the differences 

 seen in species apparently modified by the environment. Also 

 the power of spore formation under appropriate conditions 

 seems to show that the " germ plasm " and " somatoplasm " of 

 these lowlj^ organisms are not identical. 



In view of these considerations, it seems safer to regard the 

 species of bacteria as true species, doubtless variable within 

 certain limits, possibly sometimes polymorphic, but on the whole 

 comparable with species in the higher forms of life. Still the 

 absence of amphimixis must show an effect in a multiplication of 

 races (in contradistinction to varieties) in excess of the number 

 of such forms to be met with higher in the organic scale. 



The generic characters are discussed pretty full}' b}' Drs. 

 Helme and Range in the article above alluded to. The}' conclude 

 that the best characters available are the form of the elements 

 and their mode of association ; that is, they endorse the present 

 arrangement. As regards motility, they discard it. They say : 

 " ce caractere n'off"re ni assez de variete, ni surtout assez de con- 

 stance, pour apporter dans une nomenclature des donnees quelque 



