DESTRUCTION OF TYPHOID AND COLON BACILLUS. 



453 



The f(jllowiug table shows the comparative effect of the blue rays 

 and of complete shadows on the growth of the organisms experi- 

 mented on: 



roccntaf/cs of or(janisms destroyed in the inaohited half of the pJate <is coni2)ared with the 



protected half. 



From this series of experiments the following results were obtained: 



Insolation for fifteen minutes destroys to a slight extent each of the 

 three organisms experimented upon. Two hours' insolation destroys 

 08 per cent of the germs and from three to six hours kills all. The 

 colon bacillus is more easily destroyed by insolation than is the typhoid 

 bacillus. Exposure to diffuse daylight, to gaslight, or to the incandes- 

 cent electric light produces little effect. Eed, orange, yellow, and green 

 light produce little effect during two hours insolation; while the blue 

 and violet rays kill nearly as rapidly and as certainly as full sunlight. 

 Insolation from six to eight hours lessens the number of colonies under 

 the protective square to a slight extent, for the colors red, orange, 

 yellow, and green. 



Plates were made in the same manner and exposed to diffused light 

 for periods varying from fifteen minutes to two days. The exposure 

 was made on clear sunny days in the light part of a room. In this 

 experiment the result was negative, the number of colonies on the two 

 sides of the plate being approximately the same. 



An ordinary gas-burner and an incandescent light were each used as 

 the source of illumination. The i)lates were jilaced bottom ui)ward in 

 a dark room near the light used. Illumination for sixteen hours with 

 gas produced no effect on the growth of the organism as shown by 

 counting of the colonies. 



Illumination for four and one-half hours with an incandescent light 

 also gave negative results. 



A series of experiments was made with tubes of bouillon inoculated 

 with tlie different organisms and then inclosed in larger tubes contain- 

 ing tluids of different colors — red, orange, yellow, and blue — which were 

 exi)osed to sunlight with control tubes, one placed in water and the 



