HARRISON & barlow] SLIME-PRODUCING ORGANISM 



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At least one out of the two cultures was killed at each temperature 

 and for each period. Both cultures were killed by an exposure for 10 

 minutes at 65° C. 



Effect of Sunlight. — About 20 c. c. of melted sucrose agar was 

 inoculated with three large loopfuls from a blue slimy culture 5 days 

 old. The inoculated agar was poured into 4 small Petri dishes and 

 allowed to set and a strip of pasteboard about 25 m.m. wide and 1 m.m. 

 thick was then pasted across the bottom of each dish. 



The lower half of a large glass moist-chamber was floated on 

 broken ice and water contained in the upper half of the dish. The 

 plate cultures, prepared as above, were now placed, bottom up, in the 

 floating dish and the whole was exposed to the unclouded sun at 1 :24: 

 p.m., July 22nd, Latitude 43° 30." One dish was removed after 20 mi- 

 nutes and the others in the order indicated in the table. All were then 

 incubated at 18° to 22° C. 



There were no colonies visible in 24 hours, but in 48 hours there 

 were colonies in all the plates. The deep green pigmentation took place 

 in all the plates and the numbers of colonies and the pigmentation 

 were proportionate to the numbers of bacteria surviving in each exposed 

 plate, and this resulted in darkly pigmented bands in the plates con- 

 forming to the strips of pasteboard, especially marked in the plates 

 exposed 40, 60 and 100 minutes respectively. The number of colonies 

 even under the protecting strips decreased with the longer exposure, 

 probably because of light reflected from below. Colonies "numerous" 

 means several thousand jDer field of the microscope, Leitz Oc. 2. Obj. 3- 



Exposure to Sunlight. 



Conclusion. — Most of the cells are killed by an exposure to sun- 

 light of 40 minutes and all are killed in 60 minutes. 



