Abstract
At least three distinct grades of resistance to the disinfectant action of calcium hypochlorite may be recognized among the bacteria. They are respectively ordinary vegetative cells, acid-fast organisms, having a fatty composition, and the true spore cells. The present study is concerned only with the vegetative cell and the spore. Subsequent work will be done with the tubercle bacillus as representing the acid-fast group.
Pure cultures of B. coli, B. prodigiosus, B. subtilis (spore former) and B. anthracis (spore former) were grown in broth for a time sufficient for spores to appear in large numbers in the two latter cultures. A few drops were then transferred to dilution bottles, the initial number present was determined, and the calcium hypochlorite of known strength was added in carefully weighed amount. Agar plates were made at intervals and the reduction determined.
The results of the work to date may be summarized as follows:
I. The sterilizing action of calcium hypochlorite in water is very rapid at first, the maximum reduction being nearly complete in three hours.
2. Of the organisms studied, B. subtilis is most resistant, followed by B. anthracis, and then by the non-spore formers, B. coli and B. prodigiosus.
3. At least 1.5 parts of available chlorin to 1,000,000 parts of water is necessary to get 99 per cent. reduction with a spore former in six hours, while 0.5 part to 1,000,000 is sufficient for this degree of reduction with non-spore formers.
4. Sixteen parts of available chlorin per million of water does not effect complete killing of B. subtilis; 1.5 parts brings about complete sterilization with B. coli and B. prodigiosus.
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