248 PRINCIPLES AND PRACTICE OF MILK HYGIENE 



Fritzmanrfs Method. Place 2 c.c. of milk in a test 

 tube and slowly run down the side 2 c.c. of pure sul- 

 phuric acid to which one drop of a dilute formalin solu- 

 tion has been added. In the presence of nitrites a blue- 

 violet ring will form at the point of contact of the two 

 fluids, but the reaction will not occur in the presence of 

 albumen. According to Riegel a suitable formalin solu- 

 tion may be made by adding one drop of 40 per cent, 

 formalin to 300 c.c. of distilled water and mixing 15 

 grammes of this solution with one litre of concentrated 

 sulphuric acid. This method gives very accurate results 

 and is easily carried out (Rievel). 



Fresh, clean milk does not contain nitrites. Ac- 

 cording to Jensen, nitrites are not present in the milk 

 even when they have been contained in the food or drink- 

 ing water of the cow. Marcus and Huyge assert that if 

 nitrate of potassium is administered to the cow in quan- 

 tities of 5 to 10 grammes the milk sometimes contains 

 nitrates. It would seem likely that nitrates would also 

 be excreted through the udder if the cow obtained access 

 to fertilizer containing nitrates or to sacks which had con- 

 tained such fertilizer. 



The demonstration of nitrates or nitrites in milk is 

 generally regarded as evidence that water has been added 

 to the milk. Most farm waters contain nitrates and 

 nitrites, as do also some city water supplies. But Rievel 

 points out that the presence of nitrates or nitrites in milk 

 cannot be regarded as positive proof that the milk has 

 been watered, because when milk vessels are merely 

 rinsed with water containing nitrates or nitrites the milk 

 may give a positive reaction if the water is quite rich in 

 nitrates or nitrites. Tillmans says that normal milk may 



