Proteus vulgaris II. 



evident that very little, if any, modification of either of the organisms has 

 taken place as a result of the selection of slight variations in acid 

 production. In all cases, there is a slight decrease in the power to 

 produce acid, but this may be explained by the fact that the organism 

 in some cases was in contact with acid so long that all of its powers 

 may have been inhibited. In the cases where they did not come in con- 

 tact with acid at all, the power to ferment sugar was gradually decreasing 

 as a result of growth on sugar-free media. The latter conclusion seems 

 justifiable on account of the fact that organisms which have been grown 

 on sugar-free media for some time developed a higher power of acid 

 production when cultivated for a short time on media containing sugar, 

 although this power could be decreased again if the growth on sugar 

 media was prolonged, due to coming in contact with acids produced by 

 the fermentation of the sugar. 



Since, selection of slightly impressed variation in organisms Nos. 1 

 and 2 failed to produce a non-acid producing culture, the cultures which 

 orginally produced no acid were grown on media containing 2% of 

 dextrose for varying lengths of time. I succeeded in getting two cultures 

 to produce acid, but all the other cultures labeled Zenkeri and mira- 

 bilis failed to produce any degree of acidity after prolonged cultivation 

 on sugar media. It is possible that continued transferring of these 

 organisms from sugar broth to sugar broth would cause them either to 



