30 PROFESSOR LANKESTER. 



red sediment formed by the scum, excepting that its colour 

 was a little more intense. On examination with the micro- 

 scope, however, the plastids Avere found to have altogether 

 changed the character of their growth. Instead of keeping 

 down to a small size by repeated transverse fission they had 

 all increased individually in size. Some were a little more 

 than double the length of the specimens taken fresh from 

 the macerating tub, and presented two, three, or more 

 brightly red-coloured, highly refracting granules in their 

 substance, similar to those seen in the plastids drawn in 

 fig. 3, Plate III, which do not, however, represent these 

 particular specimens. This change of size and character 

 in the plastids in attendance upon change of environment 

 (removal of excessive nutrition) warrants the inference which 

 I had already drawn from the large range of variation in 

 the forms and mode of aggregation of the plastids of Bac- 

 terium rubescens — that Ave have in it (and probably also in 

 the true physiological species of colourless Bacteria, dis- 

 tributed under such form-genera as Micrococcus, Bacterium, 

 Vibrio, &c.) an example of an organism which is highly sus- 

 ceptible of change of form in response to minute changes of 

 life-conditions, and in which such changes of form have full 

 license because /orm has very little importance in relation to 

 the essential chemical phenomena Avhich characterise the 

 life of this class of organisms and give them specific limits. 



Movements of B. rubescens. — In my former account of this 

 organism I stated that I had not observed active " vital " 

 movement exhibited by the plastids except by the " acicular " 

 form. I am noAV able to modify this statement very essen- 

 tially. I have frequently observed active vital movement 

 exactly corresponding to that of Bacterium termo and B. 

 lineola in the biscuit-shajDed or bacterioid form of plastid of 

 B. rubescens. The plastids drawn in Fig. 2 formed part of 

 a growth in which nearly all the plastids were of this homo- 

 geneous character and exhibited the active darting move- 

 ment of living Bacteria. On other occasions I have found 

 growths of plastids of the character of those given in 

 Fig. 3, which also exhibited the unmistakable vital move- 

 ments known and described in other Bacteria. 



Further, I have on more than one occasion observed sIoav 

 but continuous undulating movement in the Leptothrix forms 

 of B. rubescens, such as are figured in my former paper 

 (Plate XXIII, figs. M, 25). 



The maceration variety from St. Thomas's Hospital (fig. 4) 

 also exhibits active vital movements. 



From recent study of B. rubescens and other forms of Bac- 



