tfO 



R. GREIG-SMITH. 



while Russell and Hutchinson noted certain alterations in 

 the flora but denied the destruction of the streptothrix forms. 



Be this as it may, since the protozoa are out of the ques- 

 tion, it is to the classes of micro-organisms and especially 

 to their by-products that we must look for the elucidation 

 of what constitutes the limiting factor. 



The Stimulation of Bacteria by Poisons. 



Although the action of the poisons and disinfectants in 

 stimulating the growth of yeasts and moulds has been known 

 for forty years, I believe Hiine 1 in 1909 was the first to 

 investigate the action of volatile disinfectants upon bac- 

 teria. He tested the action of fluorine, copper sulphate, 

 thymol, ether and formalin, upon the growth of Bac. coli 

 suspended in dilute bouillon. They all stimulated growth, 

 but there was a certain maximum concentration or dilution, 

 below and above which growth was diminished. The point 

 of maximum stimulation varied with the disinfectant. It 

 ranged from one part in a hundred for ether to one part in 

 ten millions for formalin. Fred 2 followed the same line of 

 investigation using copper sulphate, ether, carbon bisulphide 

 potassium bichromate and saivarsan, with all of which he 

 obtained a stimulation, when the disinfectants were 

 employed in appropriate dilutions. The ammonifying 

 bacteria were more easily stimulated than the nitrogen- 

 fixing and the denitrifying groups of bacteria. The two 

 latter groups, however, require organic matter to enable 

 their activities to be made manifest, and as this is so small 

 in ordinary soil, he concluded that the action of the disin- 

 fectants upon nitrogen-fixation and denitrification in soil 

 must be negligible. 



As the result of experiments upon plants growing in dis- 

 infected soils, he concluded that the plants were stimulated 

 directly, and at the same time an indirect stimulation was 



1 Cent. Bakt., 1 te, 48, 135. a Cent. Bakt., 2 te, 31, 185. 



