EUROPEAN FOULBROOD. 17 
same, were similar to those used in the other studies. The method 
of making the inoculations was also similar. The colonies were, there- 
fore, in the open and the bees had free access of flight. The same pre- 
cautions taken to minimize robbing, swarming, absconding, and drift- 
ing of bees were observed in the experiments with this disease as with 
the other diseases. AI] hives which had housed European foulbrood 
colonies were flamed before they were used again to be certain that 
there would be no infection from such a source. Whether the queens 
used had been in diseased colonies need not give one any concern. 
Further reference to the technique followed in the present studies will 
be made as the experiments are discussed. 
THERMAL DEATH POINT OF BACILLUS PLUTON 
The result of the experiments recorded by the writer in an earlier 
paper (16) shows that when suspended in water the thermal death 
point of Bacillus pluton is approximately 63° C., the period of ap- 
plication being 10 minutes. Further experiments have been con- 
ducted in which the organism was suspended in honey and heated. 
After being heated, healthy larve are inoculated by feeding, using 
the direct or pipette method. Table I summarizes the experiments 
made : 
TABLE I.—Resistance to heat of Bacillus pluton suspended in honey 
; A Period of : . 
Date of inoculation. Temperature. heating. Results of inoculation. 
1915. SHOE His Minutes. 
ibtaVe) Lay S) a a ee L SaS Aes See 67 153 10 | European foulbrood produced. 
UD) OSE hr eed ate Ere ean eine ones 70 158 10 Do. 
Xo) aide Sis SUS eee alpen er il ue rc 75 167 10 Do. 
CFD YE) A en cee I ES a a ee 76} . 169. 10 Do. 
ED OS Re ie, SPONSES al LBRO 3 78 172 10 Do. 
SOD fee oe een Vis Ney oe RN Ss Waa Lee 79 174 10 | No disease produced. 
AAD Rasy UN eae ee, eS al el ee ae 80 176 10 Do. 
DULTIO LS SAR IO eA Chek Bea 80 176 10 Do 
SEY OLS PAL Sc aE SHR RNa ice een inne ates 81 178 10 Do 
ITI OPO eae Mca noes Pee eben ia eR 85 185 10 Do 
COs tt a 2s eRe RN EHLEND 0 a 8 2 90 194 10 Do 
The results given in the foregoing table show that the thermal 
death point of Bacillus pluton suspended in honey is approximately 
79° C., maintained for 10 minutes. 
RESISTANCE OF BACILLUS PLUTON TO DRYING 
In conducting experiments relative to the effect of drying on 
Bacillus pluton the stomach contents (Pl. VIII) of larve sick or 
recently dead of European foulbrood are spread in a thin layer in 
Petri dishes or on slides. From time to time after the films are made 
healthy larvee are inoculated by feeding a suspension of the drying 
larval material suspended in a weak sirup solution. When no in- 
132817 °—20—Bull. 810——3 
