6Y R. GREIG-SMITtt. 183 



There was no direct toxic eflfect in any of the tests, and, so 

 far as the possibility of obtaining such by using different 

 strengths of infusion are concerned, the strongest appears the 

 most likely. The ten-days' extract of the 0-2% solution gave more 

 favourable numbers than any of the others. In this, the amoebae 

 were the most numerous. 



A further test with 0-1% hay infusion was made, but in it the 

 amcebae did not grow quite so well as on the former occasion 

 when the direct toxic action was obtained. The counts showed 

 830 per c.c. on the seventh, and 1,000 on the eighth day. No 

 evidences of toxicity were obtained on the eighth or twenty-first 

 days, and it must be concluded, that a definite toxicity cannot 

 be demonstrated by growing bacteria or amcebse in the usual 

 culture-duids. 



The Influence of Reaction. 



Much has yet to be found out regarding the influence of re- 

 action upon bacterial growth, and the reason for the rise in the 

 dilution-curves of th« extracts. As the infusions and culture- 

 solutions are generally made with tap-water to supply a small 

 quantity of saline matter accepted as being necessary for the 

 growth of micro-organisms, a beginning was made with it. Tap- 

 water is known to be alkaline, but the extent of the influence of 

 its faint alkalinity is not know^n. The nutrients were increased 

 by preparing infusions of hay, and these were made sujQEiciently 

 weak to enable useful counts to be obtained. A 1% infusion of 

 hay was diluted with 99 parts of porcelain-filtered, distilled and 

 tap-water, thus obviating heat-effects. Portions were treated 

 with lactic acid and with ammonia so as to bring up the final 

 volume to a definite reaction, and sown with a definite number 

 of cells of Bac. produjiosus. They were incubated at 22° for 20 

 hours, and counted. In tabulating the results, the highest 

 counts were taken as 100. 



