Table XVI shows the effect of a concentration of 1.0 p.p.m. of chlorine; the hypochlorite at this concentration acted almost entirely as a germicide or disinfectant.
TABLE XVI.[A]--EFFECT OF CHLORINE AS A DISINFECTANT
---------------+------------------------------ PLATED. | INCUBATION PERIOD, DAYS. ---------+-----+-----+-----+-----+-----+------ Time. |Day. | 2 | 3 | 4 | 5 | 6 ---------+-----+-----+-----+-----+-----+------ 11 a.m. | 1 | 2| 5| 7| 8| 10 12 noon | 1 | 1| 1| 2| 2| 4 2 p.m. | 1 | 0| 0| 0| 2| 2 4 p.m. | 1 | 1| 2| 2| 6| 6 10 a.m. | 2 | 0| 0| 0| 1| .. 10 a.m. | 3 | 0| 0| 0| ..| .. 10 a.m. | 4 | 5| 13| 16| ..| .. 10 a.m. | 5 | 79| 166| ..| ..| .. Untreated| | | | | | water | .. | 915|1,410|1,680|2,150|3,200 ---------+-----+-----+-----+-----+-----+------
Table XV shows a recovery of the anabolic functions after treatment with 0.1 p.p.m. of chlorine but since this was obtained by plating on such a suitable medium as nutrient gelatine, it is probable that reproduction in water having a low organic content would be still further diminished. This is indicated by the results obtained.
There is no evidence of any marked difference in the resistance of ordinary water bacteria to chlorine and these are the first to be affected by the added germicide. The common intestinal organisms are also very susceptible to destruction by chlorine and there is considerable evidence that _B. Coli_ is slightly more susceptible than many of the vegetative forms usually found in water. The specific organisms causing the water-borne diseases, typhoid fever and cholera, are, on the average, not more resistant than _B. coli_.
The spore-forming bacteria usually found in water are those of the subtilis group, derived largely from soil washings, and _B. enteritidis sporogenes_, from sewage and manure. The spores of these organisms are very resistant and survive all ordinary concentrations. Wesbrook et al.[1] found that 3 p.p.m. of available chlorine had little effect on a spore-forming bacillus isolated from the Mississippi water and the author has obtained similar results with _B. subtilis_.
Thomas,[2] during the chlorination of the Bethlehem, Pa., supply, found four organisms that survived a concentration of 2 p.p.m. of available chlorine: _Bact. ærophilum_, _B. cuticularis_, and _B. subtilis_, all spore formers and _M. agilis_.