23 



(ll) IN DIALYZED PEPTONE SOLUTION (NITRATE AND NITRITE FREE). 



As there was very little "peptone" left in bottle No. 2, 10 grams 

 from bottle No. 5 were dissolved by boiling in about 200 eubic 

 centimeters of pure water. It was then dial3^zed through parchment 

 with due precautions against introducing nitrates or nitrites or 

 any other foreign substance. As mentioned, no peptones were 

 found in the first diflfusate (six hours), which gave a reaetion for 

 nitrites. The process was continued for twenty-four hours during 

 two days, the contents of the dialyzer being removed, concentrated 

 by I)oiling, and sterilized at necessary intervals. At this time 

 10 cubic centimeters of the contents of the dialyzer gave no reaction 

 for nitrites. Dunham's peptone solution was then made up as 

 in the experiments with undialyzed "peptone" — one set being 

 marked "nitrite-free peptone" and the other "nitrite-frcp peptone 

 -pO.Ol per cent NaNOg." After autoclaving, the "nitritc-free- 

 peptone" solution gave no reaction for nitrites or nitrates, while 

 the other gave no reaction for nitrites but (juite a distinct redaction 

 for nitrates. The final reaction of this dialyzed medium was 0. 1 

 per cent alkaline to phenlophthalein, showing the removal of sub- 

 .'Jtances capable of reacting acid to })henolphthalein to the extent 

 of 0. 6 per cent. 



A series of tubes inoculated with cholera 579 was tested after 

 seventeen hours at 36° to 37°, with the following results: 



Taiu.e II. 



In about ten days, however, this dialyzed medium had absorlud 

 enough nitrites to give a distinct reaetion, and witliout the use of 

 uninoculated controls one might have assumed that the nitrites 



