514 J. HOWARD BROWN AND PAUL E. HOWE 



6. With release of calcium from citrate should produce precipitate or 

 coagulura 

 IV. Casein digestion 



a. Should give diminished or negative precipitation upon addition of acetic 

 acid. Example: Proteus vulgaris 



Various combinations of the above reactions may be observed 

 and there are doubtless other reactions which are not mentioned 

 above, for instance, with alkali production we have sometimes 

 observed a thickening of the medium into a transparent jelly. 

 This reaction was produced by Bact. alkaUgenes. 



SUMMARY 



Milk may be transformed into a transparent culture medium 

 by the addition of small amounts of various salts. Sodium 

 citrate seems to be the most suitable for this purpose. 



In such a medium there may be observed not only the ordinary 

 reactions of various bacteria in milk but also some others not 

 observed in untreated milk. 



The principal advantages of the transparent milk as a medium 

 reside in the greater visibiUty of changes which occur in it. 

 Indicators are much more easily seen in it than in opaque milk. 

 As long as the acidity remains below pH 5.5 colorimetric hydro- 

 gen ion determinations are easily made. Clouding and the 

 formation of sediment due to bacterial growth may be observed 

 as in bouillon when no visible change whatever is produced 

 in ordinary opaque milk. 



REFERENCES 



Arthus, M. 1902 De Taction anticoagulante du citrate de soude. Compt. 



rend. Soc. biol., liv, 526. 

 BoswoRTH, A. W., AND Van Slyke, L. L. 1914 Why sodium citrate prevents 



curding of milk by rennin. Tech. Bulletin 34, N. Y. Agr. Exp. Sta. 

 Sabbatani, L. 1902, 1S03 Le calciiun-ion dans la coagulation du sang. 



Compt. rend. Soc. biol., liv, 716. Le calcium dans la coagulation du 



sang (1). Arch. Italiennes de Biol., xxxix, 333. 



