INTRODUCTION 15 



shaped organism of sizes varying from 3/x to I2/^, although 

 some extended to 58/x. As Bavendanim regards Warming's 

 Bacterium sulfuratum as a composite species he was not able 

 to place the organism, and hazarded the conjecture that it 

 was a Rhahdochromatium. 



Zopf, in 1882, made a distinct advance in our knowledge. 

 He also had found an extremely variable purple-coloured 

 microbe, which he named Beggiatoa roseo-persicina. Up to 

 Zopf's time the evidence of pleomorphism had been of a 

 purely circumstantial nature, as is, indeed, the greater part of 

 biological evidence. He considerably strengthened the case 

 for pleomorphism by observing the actual transition of one 

 type of structure into another. Thus in his Spaltpflanzen, 

 Tafel 15, Figs. 3a, 3^, and 4 obviously show a stage in the 

 transition from the filamentous to the coccus form. He 

 thus observed the development of one fundamental form from 

 the other. Then again, he traced the passing of coccus forms 

 into the zoogloea condition. Zopf witnessed the actual 

 liberation of the end portion of a thread of Beggiatoa alba 

 and its conversion into a spiral structure, which on liberation 

 was observed to swim away ; in that form it was indistinguish- 

 able from a typical spirillum of the lower bacteria. If seen 

 apart, such an organism would indubitably have been assigned 

 to the genus spirillum. It is evident from Zopf's work that 

 the filamentous form, the short rod, the coccus, and the 

 spirillum may be combined in one species. 



In 1888 appeared Winogradsky's Beitrdge ziir Morphologie 

 iind Physiologie der Bacterien, which has greatly influenced 

 subsequent investigations. In this work a completely 

 different view is presented. He starts with de Bary's dictum 

 that a species is not determinable until its developmental 

 history is known. The soundness of this axiom cannot of 

 course be questioned, but there are objections to the 

 interpretations that are given to it by Winogradsky. The 

 implication is made in his writings that, if an organism is 

 put under observation under a given set of circumstances all 

 the possible, developmental phases of which it is capable 

 will be exhibited during that period. Winogradsky's method 



