CH. IV] VARIATIONS IN MORPHOLOGY 49 



isodulcite. He found that on raffinose agar B. paratyphoid 

 B strains produced papillae but B. Aertryck strains failed 

 to do so, and that this difference between the two organisms 

 was sufficiently constant to be of value in distinguishing 

 between them. The formation of papillae indicated, in certain 

 cases, the acquirement on the part of some members of the 

 strain of power to ferment the carbohydrate added to the 

 medium. 



4. Heating a strain of organisms before subculturing 

 them has been observed to modify the characters of the 

 colonies formed (Bainbridge, 1903). 



5. Finally, as a result of passage, the type of colony 

 formed by a strain of bacteria may be modified. Thus Adami, 

 Abbott and Nicholson (1899) injected into a rabbit a strain 

 of typical B. coli. The organism recovered formed on agar 

 colonies closely resembling those of S. pyogenes. By intra- 

 peritoneal passage through three guineapigs typical B. coli 

 were obtained once more. 



Variaton in other morphological characters. 



Detailed reference has not been made to variation in 

 other morphological characters, such as motility, pigment 

 formation, the development of capsules and staining properties, 

 since these are well known to vary greatly at different times 

 and under different conditions. A few examples of such 

 variation will be found in the earlier sections {vide Chap. ii). 



