490 • '' Blackleif of the Potato 



without nitrate. Nitrite was present after 24 hrs. and was still present 

 after thirty days. 



Diastatic Action. This was tested on a piece of potato standing in 

 water. After fourteen days the liquid gave a true red colour with iodine, 

 showing that all the starch had been hydrolysed. The diastatic action 

 of the organism is fairly strong despite the fact that the starch grains 

 appear to be unattacked in the cells of rotted potato tissue. 



Milk. Coagulated on the sixth day. The curd was quite loose and 

 was easily broken by gently tapping the tube. On the twentieth day 

 the whey was well separated from the curd. The curd was still present 

 thirty days after inoculation. 



Litmus Milk. Became slightly acid on the third day, distinctly so 

 on the fourth day ;■ coagulation occurred on the ninth day, loose curd 

 as above ; the whey titrated on the thirtieth day was acid to the degree 

 0-06 N (+ 60 of Fuller's scale). 



Dunham's Solution. Growth was not vigorous, only a slight tur- 

 bidity was formed. When tested after fourteen days there was no sign 

 of the presence of indol. 



Thermal Death Point. 60 c.c. of potato broth was inoculated and 

 incubated over night at 25° C. The turbid liquid was divided into six 

 sterile tubes and these were subjected for ten minutes to temperatures 

 ranging from 48° to 55° C. Inoculations made from these on potato- 

 agar showed that the organism was killed at temperatures above 49° C. 



INFECTION EXPERIMENTS. 



Sterile Slices of living Potato. The potato was sterilised with mer- 

 curic chloride, washed three times with sterile water and cut into slices 

 with a flamed knife. The slices were placed on wet blotting paper in 

 sterile petri dishes. At 20° C. rotting was well established after 24 hrs., 

 had penetrated to a depth of about 2 mm. and had spread to a radius 

 of 1 cm. from the point of inoculation ; at this temperature the whole 

 of the tissue was decomposed. The rotted tissue had a strong alkahne 

 reaction to litmus and gave off a volatile base which was identified by 

 the sense of smell as trimethylamine ; no other odour was perceptible. 

 As stated earlier the rot was perfectly white and remained so in the 

 incubator but on exposure to light a rose-pink colour developed. At air 

 temperature 12° to 14° C. the rot usually progressed throughout the 

 depth of the slice (5 to 6 mm.) but after spreading to a radius of I to 

 ] -5 cm. from the point of infection it was frequently prevented from 

 further advance by a resistant layer of cork; this cork formation was 



