Quantitative studies of salivary constituents were seldom, if ever, undertaken five years ago. This was due to the cumbersome methods then in vogue. With the application to saliva of the rapid and accurate microchemical methods of blood analysis, more attention has been directed toward the salivary constituents, and especially toward urea, as a diagnostic aid.
After the discovery of urea in saliva by Pettenkoffer and Wright,1 Picard, Poisseuille, Bechamp and Gréhant1 made a few isolated determinations. Their results were varied, probably on account of the necessity of using the old hypobromite method. The first accurate quantitative studies of urea, made by Hench and Aldrich2 and by Schmitz,3 were followed by those included in the extensive researches of Updegraff and Lewis,4 and Morris and Jersey.5 These authors have shown that the combined urea and ammonia nitrogen content of saliva closely parallels that of blood urea