in the results of experiments to determine the thermal death point of the 

 bacillus, accounted for in part by the different methods used by different 

 investigators. 



McKenzie (28) found the thermal death point by suspending silk threads 

 saturated in a beef broth culture of B. alvei containing spores. The threads 

 were allowed to dry, and introduced into melted wax, and left therein for a 

 definite time, at a fixed temperature. At the end of that time, the thread 

 was introduced into melted agar and thoroughly shaken so as to separate the 

 wax from the threads. The cultures thus made were rapidly cooled, and the 

 tubes placed in the incubator at 37°0. The following are his results : 

 At 100°C. for \ of an hour, growth. At 90°0. for J hour, growth, 



" " 1 " growth. 



" " 2 hours, growth, 



" " 3 " no growth. 



" " 4 '• no growth. 



A temperature of 50°C. did not dtstroy the spores in 24 hours. These 

 experiments were repeated with the same results, which results were criti- 

 cised by Oorneil (28), who claimed that the heat to which the bacteria were 

 exposed in melted wax was not moist but dry heat, and consequently that 

 the wax had to be heated to a high temperature and for a long time in order 

 to destroy the spores. According to the testimony of two prominent founda- 

 tion makers, the wax during the refining and purifying process reaches a 

 temperature of quite or nearly 100°O. for a short time. During the sheet- 

 ing, however, it does not reach a temperature much above the melting point, 

 say 79°C. Two other foundation makers, Dadsnt & Hunt (41), state that, in 

 refining, the wax is heated for some time to 100°C., and is kept liquid for 

 24 hoars ; eo McKenzie thinks that if these temperatures are reached in the 

 making, there is little danger of foul brood from comb foundation, as the 

 specific gravity of bacteria in the melted wax is so great that throughout 

 the process of manufacture the bacteria tend to fall to the bottom. Stern- 

 berg (42) states that the spores require for their destruction a temperature of 

 100°O. for four minutes (determined in 1887); but there is so statement as 

 to the age of the spores, In Howard's experiments (40) tubes of liquid gela- 

 tine containing spores of B. alvei were placed in an open vessel of boiling 

 water and allowed to remain therein for a definite time — " in all probability 

 the water did not reach boiling point " — and trial cultures were made at stated 

 intervals, with the following results : 



After 15 minutes — growth. 



" 30 " " 



II ^g «i <(. 



"50 " DO growth. 

 <■ 60 " " 



His trial cultures were on potato and gelatine ; but no statement is 

 made regarding the age of the spores, where they were from, or the tempera- 

 ture at which they were incubated. It is, however, evident that they were 

 not given the most favourable conditions for growth. 



I have myself performed the following experiments on the thermal death 

 point of the spores : 



Method. Test tubes containing bouillon were placed in boiling water. 

 Three loopfuls of culture were introduced into each of the tubes ; and tubes, 



