222 Kepoet of the Department of Bacteriology of the 



objection to its use in quantitative work. Although the liquefac- 

 tion is slower than on beef-extract-peptone gelatin, still at times it 

 proceeds so rapidly as to prevent any count. The most efficient 

 method found to inhibit the growth of the liquefiers without stopping 

 the growth of other bacteria is to use an incubation temperature 

 that does not exceed 18° C. It seems possible, indeed, that the 

 rapid liquefaction which has so often led soil bacteriologists to 

 regard gelatin with disfavor may have resulted from their use of a 

 temperature of 20-21° C. for incubation. With the use of a suf- 

 ficiently low temperature there has seldom been any great trouble in 

 keeping the gelatin plates seven days before counting. Low tem- 

 peratures are advisable whether the medium is to be used for quali- 

 tative or quantitative purposes, although more necessary in the latter 

 case than in the former.' 25 The asparaginate agar, on the other hand, 

 can be used even when low temperatures are unavailable. 



Table X. — Tests of Fischer's Culture Medium. 



* Counts upon the asparaginate agar and upon soil-extract gelatin that are higher 

 than the corresponding counts upon Fischer's agar are printed in bold-faced type. 



t The medium used in making this count contained 0.2 per ct. asparaginate and only 

 0.05 per ct. dextrose. 



A comparison between the counts obtained on the gelatin and on 

 the other soil media may be obtained from the figures given in 

 Tables X to XIII. Fischer's agar, in the series of tests listed in 

 Table X, gave a higher count than the gelatin three times out of 

 five, in those listed in Table XIII only four times out of twelve. 

 Lipman and Brown's agar gave a higher count than the gelatin in 



26 Liquefaction may also be checked by using 20 per ct. instead of 12 per ct. 

 gelatin. This does not seem to lower the number of colonies. 



