E. M. Doidge 41 



The apparatus is connected to the nearest supply plug or lamp 

 holder by means of a flexible cord and plug or adapter. 



The tests were made with specially uniform tubes of thin glass, 

 about 18 cm. in diameter and containing exactly 10 cc. of nutrient 

 broth. Into each of these was introduced a loopful of a 24-hours old 

 culture in nutrient broth, and they were placed in the water bath for 

 ten minutes ; at the end of the ten minutes the tubes were plunged into 

 cold water to reduce the temperature and were finally placed in the 

 incubator at 30° C. with a number of control tubes. The thermal 

 death point was found to be 60° C. when determined by this method. 



A second series of experiments was undertaken in order to determine 

 the death point of the organism in a dry condition. 



A number of sterile cover slips were smeared with a suspension of an 

 agar streak in a normal saline solution. These were dried in a sterile 

 petri dish and then exposed for ten minutes to the heat of a drying oven. 

 At the end of this time they were taken from the petri dish with a pair 

 of sterile forceps and dropped into tubes of nutrient broth. The broth 

 clouded when inoculated with cover slips exposed to temperatures of 

 120° C. and under, but remained clear if the cover slips dropped into 

 it had been exposed to a temperature of 125° C. or over. The thermal 

 death point of the organism in a dry condition, therefore, lies between 

 120° C. and 125° C. 



The organism can grow through a wide range of temperature if it 

 is provided with sufficient moisture. It grows very slowly at 5 — 6° C. 

 and also at 45°. At the latter temperature nutrient broth was feebly 

 clouded at the end of 48 hours. The optimum temperature is about 

 30° C. 



Desiccation. 



The organism will not grow without a fair amount of moisture, and 

 its growth is most vigorous on a wet medium and in a saturated atmo- 

 sphere ; on the other hand, it is very resistant to desiccation and remains 

 alive for a long time in a dry condition. 



A number of diseased leaves were dried in the air in the laboratory, 

 being merely protected from dust. They were received on the 9th of 

 June, 1913, and from that date cultures were made from them at 

 intervals of a month. On the 9th of June, 1914, after the leaves had 

 been drying for one year a vigorous culture was obtained ; it has not 

 yet been ascertained how much longer the organism retains its vitality 

 on dried leaves. 



