A Bacterial Disease of Stone Fruits 411 



Lab ferment. — In the milk cultures the casein is thrown out of solution 

 without marked acid production, which indicates the presence of a lab, 

 or rennet, ferment. 



Invertase. — Cultures of all four strains of the organism were grown 

 in filtered river water containing two per cent of chemically pure sac- 

 charose and two per cent of Witte's peptone. On the twenty-fifth day 

 all the cultures were tested for inverted sugar with Fehling's solution, and 

 every culture gave the glucose reaction. 



Thermal death point. — Preliminary tests indicated that the thermal 

 death point must lie between 49° and 54° C. The following tests were 

 made to determine the point more nearly: Six sets of twelve tubes each 

 of peptonized beef broth were inoculated with the peach organism from a 

 five-days-old-slant Hiss-glucose culture, and the tubes were placed in 

 water at a constant temperature of 49°, 50°, 51°, 52°, 53°, and 54° C, 

 respectively. The tubes were removed at the end of ten minutes, and 

 were kept at 25° C. for two weeks. At the end of five days growth had 

 taken place in all the tubes that had been exposed at 49° and 50° C. 

 Growth appeared also in three of the twelve tubes that had been kept at 

 51° C. No growth appeared at the end of fourteen days in tubes that had 

 been kept for ten minutes at 52°, 53°, and 54° C. 



The experiment at 51° and 52° C. was repeated several times with 

 different strains of the organism, and in a few instances growth occurred 

 in cultures kept at 51° C. for ten minutes. There was never any growth 

 in cultures kept at 52° C. 



The thermal death point, therefore, is about 51° C. Smith (1903) also 

 placed the thermal death point of this organism at about 51° C. 



Optimum temperature. — The optimum temperature appears to lie 

 between 24° and 28° C. Growth at 24° and at 28° C. on Hiss-glucose 

 and peptonized beef bouillon was considerably better than at 32° C. 

 Growth at 20° and at 36° C. was about the same, but was considerably 

 less than at 32° C. and much less than at 24° or 28° C. 



Maximum, temperature. — Four-days-old bouillon cultures of ten strains 

 of the organism were used to inoculate slant Hiss-glucose medium. Six 

 tubes were used for each strain; three tubes of each lot were placed in an 

 incubator at 37° C, and three were kept at room temperature. All 

 cultures, both in the incubator and at room temperature, made good 

 growth; however, those exposed to the higher temperature were of the 



