REPORT OF COMMITTEE ON DESCRIPTIVE CHART 135 



Relation to free oxygen. Provisional method. Determine by- 

 noting the presence or absence of growth in open and closed arm, 

 respectively, of fermentation tubes containing glucose broth. 

 Care must be taken to use fermentation tubes from which the 

 dissolved oxygen has been recently driven off by heating. In case 

 of gas production, this test is of comparatively little value, be- 

 cause bubbles of gas may carry the sediment up with them; 

 hence if an organism produces gas from glucose, the test should, 

 if possible, be made in the presence of some other sugar which it 

 attacks (acidifies) without gas-formation. It must be remem- 

 bered, however, that even anaerobes do not grow in the absence 

 of free oxygen except in the presence of a chemical substance 

 (such as carbohydrate) which they are able to reduce and use 

 as a source of oxygen. 



Fermentation of sugars and glycerol. This is normally to be 

 studied in fermentation tubes. Ordinarily use beef-extract broth 

 containing 1 per cent of the substance investigated; but if the 

 organism does not grow well in such broth and some medium is 

 known in which it does grow well, the latter may be used. Gen- 

 erally speaking, organisms of series I and II should be studied in 

 broth, organisms of series III and IV in some other medium. 

 Incubate organisms of series I and III at 37°, organisms of series 

 II and IV at 25°. Test ordinarily on 1st, 3rd, and 7th days, al- 

 though the best days for testing will depend upon the rapidity of 

 growth of the culture. Hence on the chart, although space is 

 given for recording reaction on three separate days, blanks are 

 left for the individual student to fill in with the days upon which 

 the tests are actually made. Inoculations should always be made 

 at least in triplicate. 



To test for acid, it is recommended that in place of the illogical 

 titrimetric method, determinations of hydrogen-ion concentra- 

 tion be made by the colorimetric method described by Clark 

 and Lubs (1917 a). In accurate research work the exact shade 

 of the indicator should be compared with that obtained in stand- 

 ard "buffer" solutions, and results recorded in terms of pH. In 

 laboratories where these standard solutions cannot be obtained, 

 it is better to record results simply as + or — , according to the 



