APPENDIX. 



It has been pointed out that the number of bacteria 

 developing from a given sample of water will be 

 largely dependent upon the composition and character 

 of the culture medium. As the nature of the medium 

 varies widely according to the method of preparation, 

 workers in different laboratories can have no rational 

 basis for comparison of results until their methods are 

 essentially uniform. 



To make results comparable as far as possible, the 

 Laboratory Section of the American Public Health Asso- 

 ciation has adopted standard methods for the preparation 

 of the commonly used nutrient media given in the follow- 

 ing extract from the report of the Committee (Fuller, 1902). 



Standard Methods for Gelatin and Agar. 



1. Boil 15 gm. thread agar in 500 c.c. 



water for half an hour and make up 

 weight to 500 gm. or digest for 10 

 minutes in the autoclav at no° C. 

 Let this cool to about 6o° C. 



2. Infuse 500 gm. lean meat 24 hours Infuse 500 gm. lean meat 24 hours 



with tooo c.c. of distilled water with 500 c.c. of distilled water in re- 

 in refrigerator. frigerator. 



3. Make up any loss by evaporation. 



4. Strain infusion through cotton flannel, 

 g. Weigh filtered infusion. 



119 



