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.

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.