That cellular elements are found normally in milk has been known for many years, but it is only comparatively recently that any importance from a public health point of view has been attached to their presence. These cellular elements being usually regarded as leucocytes or pus cells, it is natural that their occurrence in milk should be looked on as indicative of an inflammatory process in the udder of the cow or cows from which the milk was obtained. The first observers to make any attempt to arrive at the numbers of these cells in milk seem to be Stokes and Wegefarth (1) in 1897. Their method, however, was very crude, and is not suited for making a true enumeration. Stewart (2) and Slack (3) followed with a very similar method, except that special tubes were used for obtaining the deposit. This “smeared sediment method” as it is called, is, however, capable of great inexactitude. Later observers have, by the use of ordinary blood counters, made the counting of the cells in milk a scientific measurement of reasonable accuracy. To Doane and Buckley (4) belongs the credit for the first published use of such a method. Savage (5) however has made the process still more accurate by first diluting the milk before centrifugalisation, and also by counting all over the field of the blood chamber, two innovations which are of very great importance, as has been borne out by our investigations. Error is easily introduced if counting is confined to the ruled divisions of the counter. Recently, Trommsdorff 6 has used a methodbased on the measurement of the deposit obtained on rotation in agraduated tube, and this method, probably on account of its ease and speed, has found much favour in Germany. It has been severely criticised by several investigators, such as Schuppius 7 and one of us 8. Riihm 9 and some others believe that it is useful if used as a routine control method. We are of opinion that it might be used in such away as an “indicator,” but for the purposes of public health control it isquite hopeless.