CULTURE MEDIA 7 1 



of the laboratory procedure and very frequently proper judgment 

 is lacking in the application of certain details of the methods. 

 For example, there is lack of uniformity in the degree of heat 

 to be used in melting gelatin media preparatory to planting, 

 in the amount of material to be planted in each Petri dish, manner 

 of planting, time of incubating, etc. 



We hereby submit the following technique in the preparation 

 of culture media and in the methods of making cultures in plates 

 as well as in test-tubes, following very generally the suggestions 

 as given in the report of the Committee of the American Health 

 Association. 



5. Preparation of Standard Cultural Media, General Suggestions 



I. Ingredients. — Distilled water is to be used in the prepara- 

 tion of all of the standard media. The distilled water must be 

 comparatively free from bacteria and must be kept in clean 

 sterilized containers and as free as possible from mineral and 

 organic impurities. If other than distilled water is used, this is 

 to be stated and the special reasons for using it indicated. 



For making meat infusions, fresh lean meat is to be used, 

 from comparatively young animals, free from disease. Meat 

 extracts may be used in place of the meat infusion. 



Unless otherwise specified, the peptone used should be made 

 from fresh beef by pancreatic digestion. It should be dry and 

 recently made. Workers should be sure to specify the kind of 

 peptone desired. Egg albumen or fibrin peptone is not to be 

 used in any of the standard media. The article should be secured 

 from some reliable house. 



The gelatin to be used in the preparation of the standard media 

 should be of the best obtainable, the so-called French brand be- 

 ing, as a rule preferred. A lo per cent, solution should not 

 soften when kept at a temperature of 25° C. It should be en- 

 tirely free from arsenic and as free as possible from acids, micro- 

 organisms, molds, and other impurities. A good grade of gelatin 



