IOWA ACADEMY OF SCIENCES. 141 



The table which follows shows the data accumulated: 



The peptone gelatin was made up according to common 

 methods, using 10 per cent, gelatine, and making it neutral 

 to phenolphtalien with sodium hydroxide. The peptone 

 agar contained 1.7 per cent, agar, neutralized in the same 

 manner. The lactose media had 2 per cent lactose added 

 after filtering. 



It is to be remarked, that the quantitative estimates of the 

 number of bacteria are estimates and not exact determina- 

 tions, the nearest we can approach to accuracy by present 

 methods. Anyone familiar with such work is aware that 



