BACTERIAL AUTOLYSIS 557 



millipram of peptone in 1 oc. is a 0.01 per cent solution; 0.2 mgm. 

 is a 0.02 per cent solution. It is possible, therefore, to read 

 differences of 0.01 per cent. Slight cloudiness occasionally 

 obscured the color to some extent. It could often be removed 

 by centrifuging or allowing the turbidity to settle out. 



The Sorensen test 



Five cubic centimeters of the bacterial suspension were added 

 to 30 cc. of distilled water. After neutraUzation, 5 cc. of neutral 

 formaldehyde were added, and the resultant acidity titrated 

 with N/20 sodium hydroxide, phenolphthalein being used as 

 an indicator. The titrations were made immediately after the 

 formaldehyde was thoroughly mixed with the test sample. As 

 the results were to be used for comparative purposes only, the 

 titrations were expressed in the number of cubic centimeters 

 required to neutraUze 100 cc. of the undiluted suspension. The 

 amount of nitrogen in milligrams may be determined by multi- 

 plying this figure by 0.7. 



Conductivity determinations 



These were made with 10 cc. portions of the autolyzing ma- 

 terial and in a conductivity cell having bright electrodes. Ap- 

 paratus and methods conform with those in use in ordinary 

 class room work. The electrodes were not platinized, owdng 

 to the possibility of a disturbing catalytic action being exerted 

 by the finely divided platinum black. The zero pomt on the 

 Wheatstone Bridge as determined by the minunum buzz in 

 the telephone receiver was consequently not as distinct as when 

 electrodes are platinized, but it was found that with a little 

 practice duplicate readings could be made which checked within 

 2 mm. Even this slight variation was reduced by taking at 

 least six readings within the middle third of the Wheatstone 

 Bridge scale, emplojdng different resistances. The determina- 

 tions were made at 25°C. 



Tlie Van Slyke method for the determination of amino nitrogen 



This method was found to yield valuable results when cer- 

 tain necessary precautions were observed. The possibilities 



