150 LAURENCE F. FOSTER AND SAMUEL B. RANDALL 



Ph should always be taken on the broth following the final auto- 

 claving as well as at the outset of any given experiment. 

 The reason for this will appear in the experiments about to be 

 described. 



In case the broth was to contain a sterile sugar this was added 

 aseptically in 10 per cent solution to the sterile medium to avoid 

 any possibihty of sphtting the sugar through heating. This pro- 

 cedure is especially important if the broth is adjusted in the acid 

 or alkaline range as it is a known fact that glucose and other 

 sugars are altered by heating with even small amounts of acid or 

 base (Mathews, 1916). Furthermore, Mudge (1917) has observed 

 an increased titratable acidity when sugars, at least disaccharides, 

 are autoclaved with media. By adding the sugar aseptically in 

 concentrated solution no change in reaction was ever noted. 



Experiment I. The extent of the changes in hydrogen-ion co7icen- 



tration which broth media adjusted to different initial Ps 



levels undergo upon autoclaving and standing 



The unadjusted broth was divided into portions of 75 cc. which 

 were brought to values ranging from Ph 5.0 to 9.0 at intervals of 

 0.4. Five cubic centimeter amounts were then tubed and auto- 

 claved at 15 pounds for fifteen minutes after which they were 

 allow^ed to cool and Ph readings taken. The tubes comprising 

 each lot were divided into three sets, one of which was allowed to 

 remain at room temperature, another was placed in the ice chest, 

 while the third was incubated at 37°. After standing at these 

 temperatures for intervals of two, seven, and fourteen days tubes 

 were removed and Ph determinations made. 



Five series were carried through and the data obtained are to 

 be found in tables 1 to 5. 



