The old method of adulterating milk with water has very largely gone
out of practise, owing to the surveillance of city authorities, and the
passing of laws that fix legal standards, which require milk to contain
a certain percentage of fats and total solids.
[Sidenote: Evil of milk preservatives]
The chief form of criminal tampering with milk has been the use of
preservatives to prevent souring. Formaldehyde has been used very
extensively for this purpose. Formaldehyde is a poison, destructive to
all cell life, and has probably been the cause of more actual deaths
than any other form of food adulteration.