14 SULPHUR BACTERIA 



Evidence of the Occurrence of Pleomorphism in the 

 Sulphur Bacteria. 



Lankester (i) and (2) found a "peach-coloured bac- 

 terium " on decomposing animal remains (caddis worms) in 

 an Oxford laboratory. This organism [Bacterium ruhescens) 

 assumed a bewildering variety of forms, all tinted with a 

 purple colouring matter which Lankester named Bacterio- 

 purpurin, and all contained inclusions which we now know 

 to be sulphur granules. In this case we have either to assume 

 that a dozen or more different species of the comparatively 

 rare sulphur-containing purple bacteria had all settled simul- 

 taneously on the caddis worms, or that all were pleomorphic 

 variations of one or at most two or three species. Lankester 

 chose to make the latter assumption, and gave one name to 

 all the variants, namely, Bacterium rubescens. 



Warming examined the purple covering on the surface of 

 decomposing vegetable remains on the Danish coast, and there 

 found an organism of a similar protean habit. He regarded 

 it as another species of the same genus as that described by 

 Lankester, and named it Bacterium sulfuratiim. At the time 

 (1876) the number of bacteria of all kinds which had been 

 described was very small, and both Lankester and Warming 

 considered that the total number of species was very hmited. 

 Indeed, Warming deduced from his experience of Bacterium 

 sulfiiratum that all bacteria had an unlimited capacity for 

 changes of form, and could all with propriety be brought within 

 the compass of a single genus. Warming was the first to make 

 a clear pronouncement on the existence of pleomorphism, 

 although with the hmited knowledge that was then at his 

 disposal he overstated the case. The most important part 

 of Warming's contribution was his discovery of intermediate 

 forms. He figures two or three hundred varieties all found 

 in the same medium and linking up by innumerable inter- 

 mediate forms the most diversely shaped varieties. Recently 

 Bavendamm has recorded the appearance in his artificial 

 cultures of an organism which he considers as identical with 

 Bacterium sulfiiratum. This was a dull red irregular rod- 



