159 



and also in ordinary stab cultures, they have been preserved 

 for a longer time than in surface cultures. Twort & Twort 

 were able to keep Pfeiffer's bacillus alive in mixed culture 

 with other bacteria for 5 — 6 months on Dorset's egg medium. 

 I investigated the resistance to heating, in March 1920 

 in the following manner. 



On a haemoglobin agar plate fresh cultures of the strains men- 

 tioned on p. 108 were inoculated and the space between the top and 

 bottom closed with cotton wool and plasticine. The plates were 

 then sunk in a water bath for half an hour, which was kept at 

 the temperature to be investigated. The plate was taken out, dried, 

 opened and a liberal amount of each culture inoculated on a new 

 plate which was kept under observation in the incubator for 2V2 

 days. This method was veiw simple to carry out, and in other 

 ways seems to have advantages: suspension of the cultures in ano- 

 ther medium which may possibly damage them is avoided; a good 

 quantity of the culture can be inoculated which will give a good 

 chance of growth even if only a very few bacilli remain alive. 

 By a suitable filling of the inoculation needle one can ensure the 

 inoculation of any fairly constant amount of the different cultures. 

 It is also easy to be certain of a uniform heating to the desired 

 temperature. 



The experiment gave the following result: At 54.5° and 50.5° 

 all the cultures were killed. After heating to 48.5°, all grew except 

 I 1, I 20, I 21, P 15(b), P 16 and H 19(b). At 46° all the strains 

 preserved their viability; I 21 however only produced 1 colony. 



In November 1921 another experiment was carried out with the 

 same technique, with all the cultures mentioned on p. 110 but Fildes 

 agar was used. The culture was killed after having grown for a 

 day and a half. The following temperatures were employed: 54°, 

 50.5°, and 47.5°. After heating to 54° only H 314 d grew (which 

 however, did not give any growth in the experiment at 50.5°). 50.5° 

 killed all the strains except H 314 b, H 318, H 319, and H 324*). 

 After heating to 47.5° the following strains did not grow: I 57 (a, b). 

 103; I 32, 36, 37; P 14; Ms 1, 4; Me la, b; H 34, 122, 164, 176,' 

 179, 205, 261, 263, 284, 265, 269, 272, 274, 276, 280, 293, 295, 298, 

 306, 308-312, 320, 325, 327, 328, 333, 338, 341, 342, 343, 345-318, 350, 

 351, 352, GP 1; Pa 4, 5; all the others grew. It should be noted 

 that the plates stood about 6 hours after the heating before inocula- 

 tions were made from them. 



Resistance against low temperatures I have found 



* All these strains were distinctly atypical. 



