228 Report of the Department of Bacteriology. 



" synthetic agar " containing peptone, and Brown's modification 

 of the latter in which the peptone is replaced by albumin. For 

 qualitative work none of these media is as good as gelatin, but all of 

 them except Fischer's allow some differences in appearance between 

 the colonies of different kinds of bacteria. For quantitative work 

 all four are about equally satisfactory; none of them give higher 

 counts than the asparaginate agar. 



Three points are brought out plainly by this investigation: 

 (1) Gelatin media are not only better than agar media for quali- 

 tative work, but allow as many if not more of the soil bacteria to 

 produce colonies. (2) A satisfactory agar medium can be prepared 

 containing nothing of indefinite chemical composition except the 

 agar itself. (3) This agar medium and those agar media especially 

 recommended by Fischer, by Temple, by Lipman, and by Brown all 

 give quantitative results so nearly alike that the counts obtained on 

 any one of them may be compared with those obtained on any other, 

 provided the same technique of incubation be used. 



ACKNOWLEDGMENTS. 



This work was begun while Dr. H. A. Harding was bacteriologist 

 at this Station, and was completed under the direction of Dr. R. S. 

 Breed, the present bacteriologist. Acknowledgments are due to 

 them for the assistance they have given. 



