Micro-organisms of M mm k Sap 505 



+ 15 Fuller's scale. The general appearance of the cultures 

 as regards turbidity, pellicle formation and rate of development 

 indicated that the optimum reaction is very close to -f-10 Fuller's 

 scale. 



Temperature relations. — The optimum temperature was 

 determined in nutrient broth having reaction oi • i<> Fuller's 

 scale. Cultures were incubated at 20, 25, 30 and 37 C. The 

 best growth was obtained at 25 C. The maximum tempera- 

 ture was not much above 37 C. and only very feeble transient 

 growth was obtained at body heat. No attempt was made to 

 determine the minimum temperature, but growth was slow at 

 io° C. 



Thermal death point determinations were made upon a 

 very large number of cultures. For this work thin walled test 

 tubes as uniform as possible and containing 10 cc. of nutrient 

 broth were used. Inoculations were made from 18 to 24 hour 

 old broth cultures. Great care, was taken to avoid slopping the 

 unheated inoculated broth upon the sides of the tubes above the 

 level of the medium. Within an hour after inoculation the 

 tubes were placed in a water bath so that the broth was well 

 below the surface of the bath, and heated for exactly 10 min- 

 utes. The temperature was kept constant within .1° C. 1>\ a 

 sensitive temperature regulator and a mechanical agitator. 

 After removal from the bath the tubes were cooled in air and 

 placed in the incubator at 25 ° C. The results of thermal death 

 point determinations were not absolutely uniform but in nearly 

 every case the death point was found to fall between 49 and 

 50 C. A few tubes heated at 50 showed growth, and in 

 some cases growth occurred after heating at a fraction of a 

 degree above 50. In a large majority of the cases the death 

 point fell between 49.5 and 50 C. In no case did death result 

 from heating for 10 minutes at less than 48.9 C. 



Growth in carbon dio.vid atmosphere. — Tubes of nutrient 

 broth were heated to drive out the dissolved oxygen, co tied by 

 dipping in cold water, quickly inoculated, and placed with con- 



