248 PRINCIPLES AND PRACTICE OF MILK HYGIENE 
Fritzmann’s 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 
