Organisms Coiisisting of One Cell 265 



clear liquid ; those of small pox being deep-seated, tense, 

 opaque, covered with a tougli skin. There are many other 

 points of distinction, and any one familiar with the two 

 diseases can hardly fall into error when dealing with typical 

 cases at whatever stage they are encountered." ^^ 



This is the type of discriminative description that occurs 

 everywhere in the writings of biological taxonomists. It is 

 as characteristic of zoological and botanical, as it is of 

 medical "diagnoses." Yet the organic species themselves 

 implicated in the diseases are invisible under the highest 

 magnifications so far produced, the specific discriminations 

 being based exclusively on the effects arising from the dif- 

 ferent activities of the two kinds of organisms ! Now what 

 are the probabilities as to the structural attributes of these 

 invisible beings? Answering in the light of what is well 

 known about all familiar organisms, can we say anything 

 else than that the microbes of smallpox and chickenpox, not 

 only possess differentiated and coordinated parts, that is, 

 are organized, but that the two species are to some extent 

 differently organized? Nor is the evidence of specificity in 

 this case at all exceptional for ultra-minute organisms, as 

 every one knows who has given attention to the popular 

 subject of "germ-life." Some of the disease producers, as 

 those of rabies, it is true, are able to flourish in a consider- 

 able range of hosts ; but this is also the case with many pro- 

 tozoan and even metazoan parasites. The microbe of hog 

 cholera is, according to present knowledge, as closely re- 

 stricted as to possible hosts as that of any disease pro- 

 ducer w^hatever; and judging from its ability to pass 

 throucfh filters, it is one of tlie smallest of the ultra-micro- 

 scopic species. So on the whole it appears that the prin- 

 ciples of host adaptability are essentially the same through- 

 out the whole range of parasitic life regardless of size. 



But while this statement about the conformity of bacteria 

 to the general rules of species differentiation and constancy 



