Elements of Water Bacteriology.Certain bacteriologists have held that the toxic waste products of the bacteria themselves may render water unfit for their own development. Horrocks (Horrocks, 1901), Garr^(Garrd, 1887), Zagari (Zagari, 1887), and Freudenreich (Freudeiureich, 1888) have shown that an "antagonism" exists when bacteria are grown in artificial culture media such that the substratum which has supported the growth of one form may be rendered antiseptic to another. Frost (1904) has exhaustively studied the phenomenon of antagonism by exposing typhoid bacilli in collodion sacs to the action of certain soil and water bacteria growing in broth. Artificial culture media, however, offer conditions for bacterial development which are scarcely paralleled in natural waters. It is difl&cult to believe that under ordinary conditions poisons are produced of such power as to render a stream or lake specifically toxic for any particular type of bacteria. It appears indeed from the experiments of Jordan, Russell and Zeit (1904), and Russell and Fuller (1906), which will shortly be referred to more fully, that the life of typhoid germs is shorter in water containing large numbers of other bacteria than in that of greater pinrity.Horrocks (1899), too, found freshly isolated typhoid bacilli alive in sterile sewage after sixty days; ' while they disappeared in five days when B. coli was also present. These phenomena may be due, however, to a struggle for oxygen, or for food, rather than to the assumed presence of highly toxic bacterial products of which there is no independent evidence.