ON A PEACH-COLOURED BACTERIUM. 29 



shaped, filamentous, or irregular. We shall see now that it 

 may also be discoidal. I pointed out previously that there 

 was considerable variation in the size of the plastids, and 

 gave figures illustrating this. The discoid plastids now 

 to be described, whilst retaining a perfectly homogeneous 

 structure, may attain each to the diameter of -rro-th of an 

 inch, whilst the largest biscuit-shaped plastids described in 

 my former paper scarcely exceed the a^jV-o^h of an inch in 

 length. Under certain conditions it seems that very small 

 biscuit-shaped plastids (very similar in shape and size to the 

 particular form-species distinguished by Colin as Bacterium 

 termo) are uniformly produced by Bacterium rubescens. 

 A group of these is seen in Plate III, fig. 4. The plastids 

 do not exceed the Tnj.woth inch in length. In this case I 

 am able to point to a special condition of life as connected 

 with this uniform shape and small size. These are the only 

 form of Bacterium rubescens occurring in the macerating pans 

 of St. Thomas' Hospital.* They occur in immense quantity, 

 covering the bones with a red film and forming crusts on 

 the side of the vessel. It appears to me that the small 

 size of the plastids and their uniform character may be due 

 to the unconscious process of cultivation and domestication 

 to which the museum curator subjects them in his macerat- 

 ing tub. A uniform temperature is maintained, an immense 

 excess of nutritive matter is continually present of a uniform 

 character (namely, decomposing bones) ,^ and the macerating 

 tub once established is kej)t in operation for many years. 

 Under these circumstances it is not unlikely that a j)ar- 

 ticular " breed " or " race " of the protean Bad. rubescens 

 has become established, just as very possibly in other par- 

 allel cases (for instance, that of Saccharomi/ces cerevisice) 

 races or even sj)ecies of ferment-organisms have been estab- 

 lished by the unconscious operation of mankind. I made 

 some experiments with the view of ascertaining whether by 

 changing the conditions of life of the maceration-breed of 

 Bact. rubescens its form or colour could be affected in any 

 way. Some of the red scum from the macerating pan was 

 isolated and placed with distilled water in a test tube. It 

 Avas thus cut off from further accession of nutriment. It 

 was left undisturbed for three months; at the end of this 

 time no change visible to the naked eye had occurred in the 



'' The colouring matter, whicli is very rich, gave the characteristic bands 

 of absorption of Bacterio-purpuriu. 



^ It should be very explicitly stated that a large proportion of green 

 unicellular algae is present with the red Bacterium in the macerating pans, 

 intermixed with it. 



