42 TEANSACTIO>'S AND PROCEEDINGS OF THE [Sess. lv. 



of the bacteria, the different varieties and species are to be 

 looked upon as absolutely distinct and constant in their 

 possession of definite morphological characters and physio- 

 logical properties, or whether these attributes of form and 

 fimction which are known to us, and upon which as a basis 

 rests our descriptive terminology, may not be liable to great 

 variation dependent upon their external environment. We 

 know, for instance, that the beautiful red pigment, which is 

 always present in a cultivation of the Micrococcus prodigiosus 

 under ordinary circumstances, may be absolutely wanting if 

 the supply of oxygen is entirely withheld. 



But if, however, from such a cultivation, kept up for 

 innumerable generations without oxygen, a fresh culture is 

 established to which oxygen is admitted, then we shall at 

 once find that the red pigment is again formed in a normal 

 amount. It has been lately stated that this organism, if 

 grown in gelatinous media to which a minute percentage of 

 phenol is added, loses the power of producing its pigment, 

 and cannot again recover it. If this be so, and it has not 

 been yet incontestably proved, then we should be much more 

 readily prepared to believe the possibility of innumerable 

 varieties being transmitted with more or less constant 

 qualities under the direct influence of an unnatural environ- 

 ment. This convenient doctrine, however, is not likely to 

 find general acceptance, inasmuch as the observations of 

 the most reliable workers tend more and more to show that 

 the bacteria are in their ultimate species more or less constant 

 and immutable. 



In this note attention is called to the fact lliat the form 

 of growth of certain bacteria, if not of all, is liable to well- 

 defined differences, accerding to the kind of nutrient medium 

 upon wliicli it is grown, and perhaps in greater degree to 

 the density of this medium, if it be a semi-solid, and if the 

 growtli takes place as mucli in its substance as upon its 

 surface. Tlie organism to which one might look as exempli- 

 fying this is the Bacillus arhorcsccns, found as a saprophyte 

 upon the desquamating skin of scarlatinal patients (British 

 Medical Journal, June 18S6). 



If one makes an inoculation of this organism into Koch's 

 gelatine peptone, in which gelatine is present to the extent 

 of 5 per cent., tlien the resulting growtli will radiate from 



