DESCRIPTION OF THE LEAF-SPOT ORGANISM. 13 



Nitrates. — Nitrates are not reduced. 



Indol. — Indol production is feeble. 



Hydrogen sulphid. — Hydrogen sulpliid is not formed in cultures on 

 beef-peptone agar, potato cylinders, turnip cylinders, or in beef 

 bouillon or milk. 



TEMPERATURE RELATIONS. 



Thermal death point. — The thermal death point is 46° C. The 

 following tests were made: Newly inoculated beef-bouillon (+15) 

 cultures in tubes were suspended in a hot-water bath where they were 

 kept for 10 minutes at a constant temperature, then removed to room 

 temperature (20° to 24° C). First, temperatures ranging from 40° 

 to 50° C. were tried, and, the thermal death point seeming to lie 

 about halfway between, trials were again made of 45°, 46°, and 47° 

 C. More than half of the cultures exposed to 45° C. for 10 minutes 

 clouded in 3 to 5 days. Of cultures exposed to 46° C. 1 out 

 of 12 clouded after 11 days. The others never clouded. Of 20 cul- 

 tures exposed to 47° C, none clouded. 



Optimum temperature. — The optimum temperature for growth is 

 24° to 25° C. 



Maximum temperature. — The maximum temperature for growth is 

 very low, viz, 29° C. 



Minimum temperature. — The minimum temperature for growth is 

 below 0° C. 



The organism was dead after exposure for 3J days at 33° to 36° C. 

 in beef bouillon. 



EFFECT OF DESICCATION. 



When young, well-clouded beef-bouillon cultures were dried on 

 cover glasses and kept in a dark place at temperatures of 22° to 25° 

 C, 75 per cent were killed in 24 hours and 90 per cent in 48 hours. 

 All were dead in five days. 



EFFECT OF SUNLIGHT. 



Four minutes' exposure to sunlight killed all organisms in thinly 

 sown agar poured plates exposed bottom up on ice, one-half of each 

 plate being covered as a check. 



EFFECT OF FREEZING. 



Freezing by means of salt and pounded ice for two and five hours 

 in +15 beef bouillon had no effect in reducing the number or the 

 vitality of the organisms, as shown by poured-plate cultures made 

 before and after freezmg. 



Beef bouillon (10 c. c.) inoculated and at once frozen and kept at 

 temperatures of -4° to -18° C. (average —12° C.) for nine days 



225 



