34 



THE AMERICAN NATURALIST 



[Vol. L 



dividuals, which constitute his primary conceptions, and 

 the terms "life" and "living substance" are pure ab- 

 stractions. Every living being presents itself to us as a 

 sharply-limited individual, distinct from other individ- 

 uals and constituting what may be termed briefly a micro- 

 cosmic unit, inasmuch as it is a unity which is far from 

 being uniform in substance or homogeneous in composi- 

 tion, but which, on the contrary, is characterized by being 

 made up of an almost infinite multiplicity of heterogene- 

 ous and mutually interacting parts. We recognize fur- 

 ther that these living individuals possess invariably spe- 

 cific characteristics ; two given living individuals may be 

 so much alike that we regard them as of the same kind or 

 "species," or they may differ so sharply that we are 

 forced to distinguish between them specifically. Living 

 beings are as much characterized by this peculiarity of 

 specific individuality as by any other property or faculty 

 which can be stated to be an attribute of life in general, 

 and this is true equally of the simplest or the most com- 

 plex organisms ; at least we know of no form of life, how- 

 ever simple or minute, in which the combined features of 

 individuality and specificity are not exhibited to the fullest 

 extent. A living organism may be so minute as to elude 

 direct detection entirely by our senses, even when aided 

 by all the resources furnished by modern science ; such an 

 organism will, nevertheless, exhibit specific properties or 

 activities of an unmistakable kind, betraying its presence 

 thereby with the utmost certainty. The organisms caus- 

 ing certain diseases, for example, are ultra-microscopic, 

 that is to say, they have not been made visible as yet, and 

 an exact description or definition can not be given of them 

 at the present time ; yet how strongly marked and easily 

 distinguishable are the specific effects produced by the 

 organisms causing, respectively, measles and small-pox, 

 for instance, each, moreover, remaining strictly true and 

 constant to its specific type of activity; the organism, 

 whatever its nature may be, which causes measles can not 



