344 WATER HYGIENE 
both American and English bacteriologists point out the value of 
storage. The rate of death of B. typhi and B. cols in pure natural 
water has been reported by Rahn and Hinds (1914) to follow the mono- 
molecular law. Under these conditions the rate increased with the 
temperature. Oxygen was found to be harmful to B. colt but bene- 
ficial to B. typhi. 
The viability of Microspira cholere has also been investigated by 
Houston using the same technique as for B. typhi. Ninety-nine per 
cent of the cholera organisms perished in three days under the labora- 
tory conditions of the experiment. This is a much shorter period than 
required for B. typhi. Gelarie (1916) studied the longevity of Micro- 
spira cholere in water of New York Bay. He stated that the survival 
of these organisms in water depends upon the strain which is used, the 
number of bacteria seeded and other factors. The organisms are said 
to live in native bay water from 7 to 45 days and in sterilized bay water 
up to 285 days. In sterile tap water they lived for from 1 to 18 days 
and in native tap water from 1 to 3 days. In competition with the other 
water organisms the life of the cholera organisms was found to be short. 
The other phase of the stream pollution question has been con- 
cerned with nuisances resulting from overloading the stream with 
sewage or organic industrial wastes. It is now fairly well established 
that rivers do purify themselves but it is more often a difficult question 
to determine the length of time required. Practically every river is 
able to handle a certain amount of organic matter. Phelps (1914) has 
stated that three factors are involved—the oxidizing bacteria, organic 
matter and oxygen. Since the organic matter and bacteria are always 
present, “the questions of stream purification and prevention of nui- 
sance reduce to one of oxygen supply.” 
Solution of Atmospheric Oxygen in Water. The amount of oxygen 
in the water which is available for the oxidizing bacteria is the important 
question in stream purification. Especially so is the extent to which 
the oxygen content may be reduced before putrefaction sets in. As 
long as there is sufficient oxygen, the bacteria will carry to completion 
the oxidation of organic matter but when this oxygen is reduced to a 
certain point, putrefaction sets in and this is always accompanied by 
foul odors. As long as the available oxygen is sufficient, the bacteria 
will carry it over to the organic matter always driving the reaction in 
that direction and not allowing an equilibrium to be established. The 
greater the speed of this reaction, the greater will be the amount of re- 
aeration which will take place and Phelps (1916) has stated that this is 
the important factor in stream purification and that dams and rapids 
