New York Agricultural Experiment Station. 211 



The sole form of organic nitrogen in this agar medium is sodium 

 asparaginate. The formula is given in Table I (p. 203). It is much 

 like the formulae recommended by Lipman and by Brown, its 

 principal differences being that nitrogen is furnished in the form of 

 definite chemical compounds only (sodium asparaginate and 

 ammonia phosphate), that it contains only 0.1 per ct. instead of 

 1 per ct. dextrose, and that it contains the ions Ca and CI which 

 Lipman and Brown do not use. 



In the preparation of the asparaginate agar, the dextrose and 

 sodium asparaginate have been added just before sterilization, so as 

 to avoid any possible effects of the preliminary heating on these 

 substances. The reaction has always been carefully adjusted; 

 because if the acidity is as high as 1.5 per ct. normal (using 

 phenolphthalein as an indicator) the count is appreciably lowered 

 (see Table VIII, p. 219). If it is as low as 0.5 per ct. normal, there 

 is danger of decomposing the ammoniun phosphate and losing the 

 ammonia. The reaction should be between 0.8 per ct. and 1.0 per ct. 

 normal acid to phenolphthalein. 23 



Considerable difficulty has been experienced in clarifying this 

 medium by the ordinary procedure, using the white of egg. Suffi- 

 cient clarification can be accomplished, however, by heating the 

 medium half an hour at 15 pounds steam pressure in such a way 

 as not to disturb the sediment, and then decanting through a cotton 

 filter. This method of clarification is simpler and is really prefer- 

 able to the use of white of egg, as it does not introduce into the 

 medium any material of indefinite composition. 



TESTS TO DETERMINE THE MOST SATISFACTORY FORMULA. 



The exact formula given for this agar in Table I is not to be con- 

 sidered as the only satisfactory combination possible. Tables IV 

 to VIII show the results of a few tests bearing on this point. The 

 conclusions that may be drawn from these tables are somewhat 

 limited by the small number of tests made. The same irregularity 

 between different batches of the medium already mentioned for 

 gelatin probably also occurs with the agar. The differences shown in 

 these tables between the counts obtained upon the different media 

 are undoubtedly less than those that might be obtained with different 

 batches' of the same medium. The small number of tests made, 

 therefore, can furnish only indications. To establish any actual 

 difference between the various media would require a long series 

 of tests, for which time was lacking in the present investigation. 

 Lack of time has also made it impossible to test out any but the most 

 significant points. 



The first point tested was to determine the most satisfactory 

 amount of asparaginate to use. It was found possible to vary this 

 considerably without affecting the results. This is shown by the 

 first four columns of Table IV. The usual formula containing 0.1 



23 This ordinarily requires just 10 c.c. of normal sodium hydroxide per litre. 



