5 



the limited time at my disposal, a historical sketch of the 

 development of the question, and shall endeavor to pre- 

 sent merely the present knowledge of the subject, with 

 a review of the evidence upon which it rests. 



Fungi plants which, because devoid of chlorophyll 

 and therefore unable to fabricate the necessary hydro- 

 carbons, are usually parasitic upon animal or vegetable 

 tissues, living or dead may be divided into three general 

 classes : i, the mould fungi (aspergillus varieties, for 

 example) ; 2, the budding fungi (e.g. t the yeast plant) ; 

 and, 3, bacteria, or dividing fungi. 



Bacteria were denned in 1875 by Cohn as "cells de- 

 void of chlorophyll, of spherical, oblong, or cylindrical, 

 sometimes twisted or sinuous form, which reproduce 

 themselves exclusively by transverse division and live 

 either isolated or in families." This definition requires 

 to-day but one modification ; reproduction, namely, is 

 known to occur in several species, at least by the forma- 

 tion and liberation of spores as well as by fission. The 

 bacteria consist of a nitrogenous, highly refractive, usually 

 colorless substance, protoplasm or mycoprotein (Nencki), 

 imbedded in which glistening, oily looking granules can 

 sometimes be observed. The bacterium exhibits a power 

 of resistance toward acids and alkalies which could not 

 be possessed by a nitrogenous substance ; hence it was 

 assumed by Cohn that the external layer is a sheath of 

 cellulose or similar hydrocarbonaceous material, such as 

 the mould-fungi are known to possess. Although there 

 has been as yet no decisive ocular demonstration of the 

 existence of this membrane, the reactions of certain spe- 

 cies toward straining fluids corroborate the assumption. 



Many of the elongated bacteria have been demon- 

 strated to possess also a thread like projection from the 

 extremity, a flagellum or cilium ; these, as well as- some 

 other varieties not yet proven to possess flagella, are 

 capable of independent, often rapid locomotion in liquids; 

 others are devoid of flagella, and incapable of motion ; 

 hence it is highly probable that the power of locomotion 

 is associated with the possession of cilia. Beyond this 



