914 EXPERIMENT STATION RECORD. 



a media in which the bacteria were growing to the temperature of the 

 liquefied air, submitted the organisms to a cooling process in the form 

 of broth emulsion in hermetically-sealed tubes. In this experiment 

 the tubes were kept practically at —190'-^ C. for 7 da3\s; after which 

 they were carefully thawed, opened, and the contents transferred to 

 suitable culture media. The organisms employed were BacjUux 

 typhosus^ B. coli com'munis^ B. diphtJierice^ B. jrrotetis vulgaris^ B. 

 acidi lactici^ B. anthrads (sporing culture), B. 2)hosjj}iorescens^ Spi- 

 7'illum cholercB asiaticcp^ StaphylococmH pnjogenes aureus, a Sarcina, a 

 Saccharom3X'es, and unsterilized milk. Cultui'es made at the conclu- 

 sion of the experiment grew well, and in no instance could any impair- 

 ment of the vitality of the organism be detected. In one or two in- 

 stances growth was slightly delayed, an effect which might have been 

 due to other causes. The photogenic bacteria grew and emitted light, 

 and the samples of milk became curdled. 



Effect of different degrees of light on the multiplication of 

 ■water bacteria, F. T. Bioi.etti {California Sta. Rpt. lS9S,pjj. 174- 

 177). — In order to throw light upon the question of whether the water 

 of a storage reservoir could be best conserved from bacteral contami- 

 nation ])y exposure to the direct sunlight, or by being roofed over to 

 exclude the direct sun raj's, or by being completely covered so as to 

 leave the water in darkness, the author undertook a series of experi- 

 ments in which samples of water were taken from the inlet of the 

 reservoir, placed in glass dishes, 10 in. in diameter and 4 in. in depth, 

 and kept under different conditions, viz, exposed to the direct sun- 

 light, exposed to diffused light only, kept in a dark cup1)oard. covered 

 with a thin layer of crude petroleum, and alum and lime or alum and 

 salt added to precipitate the material in the water. In the latter cases the 

 dishes were kept in diffused light. The bacterial content of different 

 samples was determined at intervals, the number of bacteria in a cubic 

 centimeter being shown in tabular form. The experiments showed 

 that there was little difference in the bacterial content of the impure 

 water, whether exposed to direct sunlight or kept in darkness, though 

 what little difference there was was in favor of the sunlight. The 

 effect of direct sunlight on certain bacteria is well known, but the 

 author doubts whether this effect will extend to the lower parts of a 

 deep reservoir. In practice the inconvenience attending exposure to 

 direct sunlight more than overbalances the slight gain in the prevention 

 of bacterial growth. Where the water was kept in the direct sun- 

 light, there were many colonies of diatoms formed and various algge 

 grew at the bottom. The trouble from algte in pipes and filters makes 

 the prevention of their growth very desiral)le. Where the water was 

 covered with a slight film of petroleum, none grew. 



The effect of precipitation of l)acteria by means of small quantities 

 of alum and lime was quite marked. Impure water was rendered pure 



