34 METHOD OF DESTROYING ALG^ IN WATER SUPPLIES. 



the copper in solution. At room temperature, wiiich i.s near the tem- 

 perature of a reservoir in summer, a dilution of 1 to 100,000 is fatal to 

 typlu in three to five hours; at 5^ it requires twenty-four hours for 

 complete destruction. 



The results obtained were checked in three ways: 



(1) Five cubic centimeters of each of the solutions to be tested, 

 made up with filtered hydrant water and check tubes of the same 

 water, were sterilized in test tubes. To each of these was transferred 

 one 3-mm. loop of a bouillon culture of the bacillus. After the proper 

 exposure, a 3-mm. loop of the inoculated water from each tube was 

 transferred to a sterile bouillon tube with a corresponding number. 

 These bouillon tubes were then incubated fortv-six hours at 38*^, the 

 time and concentration of the agent required to prevent growth being 

 noted. 



(2j Instead of transferring to bouillon tubes from the inoculated 

 water, the transfer was made to gelatine tubes, and plates were poured 

 in 10-cm. Petri dishes, thus making it possible to estimate the reduc- 

 tion in the number of bacteria in concentrations not sufficient to pre- 

 vent growth, 



(3) Five 12-liter aquaria, two of which contained a high percentage 

 of organic matter, also a large quantity of algw and other aquatic 

 plants, were inoculated, each with 3 cubic centimeters of cultures of 

 Bacillus typhi of different ages, and allowed to stand eighteen hours, 

 and two poured plates were made from each aquarium, the 3-mm. loop 

 being used in all cases. To these aquaria were then added a 1 per 

 cent solution of copper sulphate in sufficient quantity to produce the 

 desired concentration. After the proper time had elapsed, another 

 series of plates was made, this being repeated ever}^ two hours for a 

 period of twelve hours. 



The tests were made upon four distinct cultures of Bacillus typhi^ 

 designated respectively Wasserman, Stokes, Say, and Longcope, and 

 except in the case of the aquaria series, upon Bacillus coli and some 

 of the para forms. These organisms were obtained from the labora- 

 tory of H. K. Mulford & Co. 



ASIATIC CHOLERA. 



The method of procedure in determining the toxic concentration for 

 Microsjnra comma {Spirillum choleree) was identical to that employed 

 in the case of Bacillus typhi. The tables on the next page show that 

 the toxic limits of these two pathogenic organisms are ver}- similar and 

 that Microspira comma is slightly more sensitive to copper sulphate 

 than is Bacillus typhi. To destroy the cholera germ requires about 

 three hours in a 1 to 100, COO solution at a temperature above 20^. A 

 longer exposure or a higher concentration is necessary to produce this 

 result at lower temperatures. 



