Methods for the Quantitative Determination of the Non-Protein Nitrogenous Constituents of Milk

About a year ago work was commenced on a study of the nonprotein fraction of milk.When this investigation was planned it was believed that the methods now in use for the determination of the non-protein constituents of blood could be used with advantage for the analysis of milk.Preliminary experiments soon proved, however, that our supposition was incorrect.The relatively large amounts of lactose and of fat present in milk, and the difference in the chemical propertiesof the proteins of milk as compared with those of blood, have made it necessary for us to spend a considerable amount of time on working out analytical met.hods to fit our needs.The methods described below have been used by us in the examination of a considerable number of samples of cow's and human milk and with this material have given good results.Total Non-Protein Nitrogen.A necessary preliminary to the det.ermination of non-protein nitrogen in milk is a procedure for removing not only the protein, but also lactose and fat.The necessity of complete removal of protein is obvious, and, while it might be possible to devise some