TRANSPARENT MILK AS A BACTERIOLOGICAL 



MEDIUM 



J. HOWARD BROWX and PAUL K. HOWE 



From the Department of Animal Palholnciij of The Rockefeller Insliiute for Medical 

 Research, Princeton, New Jersey 



Receiver! for publication February 10, 1922 



The addition to milk of an oxalate or a citrate, in the form, for 

 example of a sodium salt, will cause the opacity of milk to disap- 

 pear and give a solution which is opalescent in thick layers but 

 almost clear in thin layers.' A similar result may be obtained 

 with sodium sulphate when added in relatively larger amounts. 

 This change is particularly evident when the milk is diluted 

 slightly, .\lthough we have not found the phenomenon de- 

 scribed in the literature it may have been observed by those who 

 for infant feeding have added sodium citrate to milk to prevent 

 rennet coagulation. The general nature of the reaction has 

 been known and the procedure has been used to prevent the coagu- 

 lation of blood. Arthus (1902) showed that sodium citrate in 

 the proportion of 2 to 3 parts per 1000 would prevent the coagu- 

 lation of milk by rennin. Bosworth and \'an Slyke (1914) in 

 a study of "wlu' sodium citrate prevents curdling of milk by 

 rennin" found that there was an increase in the amount of solu- 

 ble calcium which would pass through a Chamberland filter with 

 increasing quantities of sodium citrate until approximately 1 gram 

 of the hydrated salt had been added to 100 cc. of milk. Rennin 

 coagulation was prevented when 0.4 gram of the citrate had been 

 added to 100 cc. of milk. The failure to coagulate in the presence 

 of citrates was ascribed to the formation of calcium citrate or 

 sodium-calcium citrate. 



The loss of opacity is apparently due to the removal of the 

 calcium combined with casein or globulins in milk. The addition 



' Howe, Paul E., unpublished work. 



511 



