202 Report of the Department of Bacteriology of the 



show a slight superiority of this albumin agar both over Lipman 

 and Brown's earlier medium and over Temple's agar. 12 Each of 

 these media has been recommended by a different investigator, and, 

 beyond the tests made by Brown, no comparison between them 

 seems to have been published. 



The little weight which the authors of these media have attached 

 to the matter of distinctions in appearance between different kinds 

 of colonies is shown by the fact that they have scarcely ever recom- 

 mended the use of gelatin media. A few investigators, it is true, 

 such as Hiltner and Stormer 13 used the ordinary beef-extract-peptone 

 gelatin. Hoffman 14 similarly used a beef-extract-peptone gelatin 

 with soil-extract. Fischer 15 mentioned rather casually the use of 

 a gelatin medium containing nothing but gelatin, soil-extract, and 

 1 per ct. of dextrose, but does not recommend its use on account 

 of the low and irregular counts obtained upon it. A modification 

 of Fischer's formula (containing 0.1 per ct. instead of 1 per ct. dex- 

 trose) has been used by the writer with very good results. The 

 use of this last mentioned formula has been referred to already 

 in several publications; 16 but no counts have yet been given to 

 show how this medium compares with others. It is the gelatin 

 medium to which particular attention is to be given in the present 

 paper. 



The use of soil-extract, peptone or some other substance of 

 unknown chemical formula in all of these media shows how little 

 stress has been laid upon the importance of having culture media 

 of definite chemical composition. Lipman and Brown's medium 

 alone is fairly satisfactory in this respect. Its authors, indeed, 

 speak of it as a " synthetic " agar, in spite of the fact that it con- 



13 The following is a summary of the six tests, taken from Brown's tables (loc. cit.) : 



13 See footnote 2. 



14 See footnote 0. 



15 See footnote 7. 



16 Conn, H.J. Bacteria in Frozen Soil. Centbl. Bakt., Abt. II, 28:422-434, 1910. 

 Bacteria of Frozen Soil, II. Centbl. Bakt., Abt. II, 32:70-97, 1911. A Classification 

 of the Bacteria in Two Soil Plats of Unequal Productivity. Cornell Univ. Agr. Exp. 

 Sta.,Bul. 338:65-115, 1913. Bacteria of Frozen Soil. N. Y. Agr. Exp. Sta., Tech 

 Bui. 35:1-20, 1914. 



