336 On Certain Bacteria from the Air of New York City. 



peared, resulting growth wrinkly with a considerable soft edge^ 

 3, from a deep colony (characters therefore not known), resulting 

 growth about half wrinkly, half soft, mixed; 4, from the smooth 

 border of a colony, resulting growth all of the normal soft form. 

 These results are equally well explicable as the results of con- 

 tamination as of reversion. 



Next plates were prepared from tube No. 1, just described. 

 As no soft border was detected, the growth was presumably, but 

 not positively, of the pure wrinkly form. The resulting colonies 

 were obtained twenty-five on two plates, and consequently well 

 separated. Most of them were of the very wrinkly form with 

 uneven contour and folded surface, and several of these exhibited 

 the soft border in varying degrees. In some it was all around: 

 in others, on one side onh% and in one the colony was half soft, 

 half wrinkly. About a quarter returned to the original form of 

 colony with granular surface and rim-shaped margin, and these 

 had no soft borders. No pure normal, soft colonies were seen. 

 The agar tubes made from the ver}' wrinkly colonies and the 

 rimmed-margin ones were scarcely to be distinguished at a casual 

 examination ; but a closer observation showed slight differences of 

 the same nature as those betwen the two forms of colonies. The 

 difference is so slight, however, and so soon becomes obscured by 

 the advance in growth, that I did not notice it previously in the 

 investigation, though it must evidentl}- have obtained. 



At this stage of affairs, we have presented the following alter- 

 natives : either the A^ariations which I am trying to establish or 

 disprove do occur, or the following condition is operative. It is 

 conceivable that when the skinny growth of the wrinkly form is 

 agitated in sterilized water preparatory to making plates, that on 

 account of its propert}^ of coherence, instead of becoming sepa- 

 rated into individual cells, certain of which are subsequently to- 

 develop colonies, the smallest portions really consist of masses of 

 cells which might entangle a few cells of the smooth form, if this 

 were originally present as a contamination. Thus the resulting 

 colonies might be impure and the apparent phenomena of rever- 

 sion be due to a sepai-ation of this mixture. Now the phenomena 

 described above, of the soft borders to the wrinkly agar cultures 

 and colonies, are in favor of this view, and it was also observed 

 that the growth when shaken up in water disintegrated Avitli 

 great difficult3\ On the other hand, the existence at this time of 



