366 



H. M. Vernon 



species were made by Russell >, and also by B. Fischer 2, wbo found, 

 as had Buchner for fresh water g-erms^, that diffuse dayligbt bad a 

 certain amount of germicidal power, as well as direct sunligbt. 

 Fischer indeed sbowed tbat tbe numbers of baeteria in specimens 

 of surface sea-water collected in the evening, after tbe whole day's 

 exposure to the sunlight, were considerably smaller tban iu those 

 taken in the morning. In tbe present research tbe numbers of baeteria, 

 in various specimens of water, variously treated, were determined by 

 tbe ordinary gelatin piate culture method. As tbe observations were 

 begun in tbe summer, when tbe temperature of tbe moist Chamber 

 remained at about 25° — 26° it was thought better, as tbe weather 

 became colder in tbe autumn, to continue to keep tbe cultures at tbis 

 same temperature. Hence tbe temperature of tbe Chamber was artifi- 

 cially kept up to tbis point by means of a gas tlame and regulator. 

 The bacteriological exaraination consisted merely in determining- tbe 

 numbers of colonies formed after 24 and 48 hours respectively, and 

 no attempt was made to isolate and study the various bacterial forms. 

 With regard to tbe ett'ects of sunligbt on water, the bactericidal 

 action noticed by previous observers was confirmed. Thus on ex- 

 posing a flask full and a covered jar half full of tbe Aquarium water 

 to sunlight, for some days, tbe following numbers of baeteria per 

 cubie centimetre were found. 



Here we see that after four days exposure, the number of baeteria 

 was considerably diminished in one case, but in the other only tbe 

 rapidity of growtb of tbe colonies was affected, tbe actual number 

 of colonies after 48 hours development being increased. After ten 

 days exposure to tbe sun bowever, tbe numbers of baeteria present 

 were in each case enormously increased. The sun was not very 



1 The Botanical Gazette Vol. 18 1893 pag. 414. 



- Die Bakterien des Meeres, in: Ergebn. Plankton-Exped. Bd. 4 M 1894 

 pag. 55. 



3 Arch. Hyg. 17. Bd. pag. 197. 



