VIII, B, 1 Walker: Balantidicidal Activity 5 



Balantidium coli has been found to be extremely sensitive 

 to changes in the tonicity of the medium in which it is placed. 

 It was, therefore, necessary to determine the most favorable 

 tonicity of the fluid to be employed in making the dilutions 

 of the drugs and chemicals in order not to introduce a source 

 of error from this factor in the tests. It was found that 0.85 

 per cent normal physiological salt solution was slightly hyper- 

 tonic, while distilled water was slightly hypotonic, for Balan- 

 tidium coli. Therefore, comparative tests were made with 

 different strengths of sodium chloride solutions, and it was 

 decided that 0.5 per cent solution represented about the optimum 

 tonicity for this organism. A departure from the use of 0.5 

 per cent sodium chloride for making the dilutions was found 

 to be necessary in certain cases. Thus, in the case of mercuric 

 iodide, which is not soluble in water or physiological salt solu- 

 tion, a 2 per cent solution of potassium iodide in water was 

 employed for dissolving and making the first dilution of 1 in 

 50; the subsequent dilutions were then made with 0.5 per cent 

 sodium chloride solution. In this case the first and consequently 

 the subsequent dilutions contained the same percentage of potas- 

 sium iodide as of mercuric iodide. A series was then run with 

 potassium iodide as a control, which was found to be inert. 

 Again, in testing some of the compounds of silver, which are 

 precipitated by weak solutions of sodium chloride, the dilutions 

 were made with distilled water and a control run with dis- 

 tilled water. 



In the preliminary tests of each substance dilutions of 1 in 50, 

 1 in 500, 1 in 5,000, and 1 in 50,000 were made. These, when 

 mixed with equal parts of the fluid faeces containing the balanti- 

 dia, gave final dilutions of 1 in 100, 1 in 1,000, 1 in 10,000, and 1 

 in 100,000. The limits of the balantidicidal action of the sub- 

 stance between any two of these dilutions having been deter- 

 mined, the more precise limit of its action was then determined 

 by making intermediate dilutions between the highest positive 

 and the lowest negative dilutions. 



Dilutions of the substances to be tested were made in the 

 following manner. If, as in most cases, the substance was a 

 solid, 0.2 gram was weighed out with an analytical balance 

 in a 10 cubic centimeters volumetric flask. The substance was 

 then dissolved with 0.5 per cent sodium chloride solution and 

 the flask filled to the graduation mark. This gave a dilution 

 of 1 in 50. If, as was rarely the case, the substance was a 



