25 



No. V, which showed no pigment, and, as I was informed, had not 

 for at least two months back. The first result on 48 hour agar 

 plate was: 



B. prod. IV, 200 small colonies, apparently all orange red. 



B. prod. V, 2 pink colonies, 48 white. 



B. prod. VI, 300 to 400 colonies, all red. 



B. prod. VII, 35 soft spreading white colonies, 3 pink. 



B. prod. VIII, 5 smooth round colonies, all violet red. 



All the agar streak inoculations from red colonies, and some 

 from white ones, gave ordinary red cultures of varying intensity; 

 and it was evident that the number of abnormal white colonies which 

 appeared as "sports" on the plates were in each case only an indi- 

 cation of the degree to which the colorless variations of the original 

 cultures had gained an ascendency over the red type through con- 

 tinued unfavorable conditions, probably because of long intervals 

 between transferences. That this was the case was shown by a 

 second plating after rejuvenation, fifteen days later. The results of 

 this were: 



B. prod. IV. 400 brilliant vermilion colonies. 



B. prod. V, 50 violet red colonies, 5 white ones. 



B. prod. VI, all red. 



B. prod. VII, 683 colonies, some spreading, all vermilion. 



B. prod. VIII, 26 smooth violet red colonies, 1 white. 



There are, however, exceptions to the good results of rejuve- 

 nation, unless plating and careful selection of colonies is a part of 

 the process. It sometimes occurs that an old culture on neutral agar 

 which has stood in the stock case two or three months will give a 

 brillant pigment on the first transference to neutral agar again, while 

 successive inoculations will seem to diminish the pigment production. 

 The first vigor may be the result of natural selection, but I have 

 no explanation to offer for the later deterioriation in this case. 



Light colored or colorless colonies which appear as discontinuous 

 variations upon plates often give rise to apparently constant varie- 

 ties. Such a colony of B. ruber miquel produced a luxuriant 

 white agar streak, which showed only a few pin-point dots of red. 

 This was allowed to grow for several weeks, and the next and 

 several future transfers gave pure white cultures with all the other 

 characters of B. ruber miquel. Davis 1 ) notes "sports" of B. r o s a - 

 ceus metalloides which gave rise to dark and to light colored 

 varieties. 



Among my series several instances of discontinuous variation in 

 mass cultures have appeared. A "crusty" variety of B. amylo- 

 ruber occurred, as in the case of Dyar's B. lactis erythro- 

 genes, after a summer's storage. The original culture had not 

 become contaminated, the pigment of the wrinkled crusty culture was 

 identical in violet red color and rapidity of development with that 



1) Davis, N. F. (Science, Vol. XIII. 1901. p. 324.) 



