Report on the Bacteriology of Water. 3(51 



A point of great importance arises here not for the first time, 

 but very vividly. That is the gradual, and much slower, but, 

 nevertheless, determined reduction of the spores, even in the dark 

 flask. I am convinced that the principal factor in this is the 

 changes in temperature undergone by the water, which was warmed 

 up to 30 C., or thereabouts, during the day, and cooled to 4 or 

 5 C., or even lower, during its stay on ice. 



XIX. 



The following experiment (Table P) gives an excellent example of 

 how much can be done by the clear sun of a hot summer day in 

 clearing the water of living spores of anthrax. 



A quantity of anthrax spores were carefully rubbed up in about 

 50 c.c. of sterile-distilled water, on August 16, and the infected 

 water distributed into two Erlenmeyer flasks, marked Aa; and Ba:. 



Aa; was exposed to the sun, with a mirror belo<v and behind, from 

 10 A.M. to 4 P.M., and the sun during the whole period was brilliant. 

 Brc was placed beside Ax, but carefully shut in an opaque wooden 

 box. 



A sample plate was taken from each flask before exposure, and, 

 after twenty-five and a half hours' incubation at 22 25 C., gave the 

 following numbei-s. Plate from Ax = 23,000 colonies = 897,000 

 per c.c., the plate beginning to liquefy. Plate from Ba;, after the 

 same incubation, was already in an advanced stage of liquefaction, 

 but we satisfied ourselves of at least 5000 visible colonies = 170,000 

 per c.c. Total of the two, 1,067,000 ; mean, 533,500, as the minimum 

 number per c.c. 



At 4.15 to 4.30 P.M., after six hours' bright insolation of the ex- 

 posed plate, two sample plates were taken from each flask. 



Those from Aa; (exposed) gave 117 and 40 colonies respectively 

 as the maximum numbers we could discover after 72^ hours' incuba- 

 tion, beyond which we could not carry the process. The counting 

 was doiie twice every day, and every colony actually marked. These 

 numbers give us 4563 and 1360 per c.c. as the maximum; total = 

 5923 ; mean = 2961 per c.c. 



On the two plates from Ba; (not exposed) we found at least 5900 

 and 6600 respectively, after repeated countings of all the squares. 

 Moreover, these numbers were obtained in forty-eight and a half 

 hours, the liquefaction being so pronounced later that we could not 

 count farther. We thus get a minimum of 200,600 and 228,400 per 

 c.c. ; total, 429,000 ; mean, 219,500 per c.c. 



Even admitting as of course we do that these numbers can only 

 be approximations, it is at least clear that the bactericidal power of 

 the sun's rays, even on the spores in sterile water, is far more 



