1. _Preparation of Microscopic Slides._ This course might at once occur to the mind as the first to adopt in searching for bacteria in milk. Devices have accordingly been proposed for saponification previous to staining. Some recommend the addition of a few drops of a solution of sodium carbonate; others use methylene blue and chloroform. But, whatever plan of staining is adopted, this method of examination in its simplest form is in no degree a criterion of the bacterial content of a large quantity of milk. Hence it has come to be recognised that one of two manipulations must precede such microscopic examination. These simple processes are known by the terms of _sedimentation_ and _centrifugalisation_. Sedimentation means merely placing the milk in conical glasses in a cool place for twenty-four hours. The introduction of improved forms of the centrifuge has brought the second method of securing a sediment into preference. Five cubic centimetres of the milk are introduced into the graduated bottle, which is then placed in the centrifuge, and whirled for one or two minutes. Thus a deposit of particulate matter is ensured. Cover-glass specimens of the sediment or deposit are then prepared and stained in the ordinary way. [Illustration: A CENTRIFUGE Used in the Examination of Milk] In testing for tubercle something more is generally necessary. To the 50 cc. of the milk set aside for sedimentation 10 cc. of liquefied, colourless carbolic acid are added. The mixture is shaken and poured into the conical glass. After standing for twenty-four hours a little of the sediment is taken by means of a pipette and examined by ordinary methods, though after "fixing" the films with heat they are some times passed through equal parts of alcohol and ether. The stain is of course that usually adopted in tubercle, namely, the Ziehl-Neelsen. Scheurlen suggested a method for demonstrating the tubercle bacillus in milk by steeping the cover glasses first in alcohol and then ether, after which they were stained with Ziehl-Neelsen. 2. _Plate Culture._ The milk is to be diluted a thousand or more times with sterile water, and ordinary plate cultures made in Petri dishes or flat-bottomed conical flasks. The colonies should be counted as late as possible; but even then the isolation of pathogenic germs is uncertain. As regards further procedure, the ordinary methods of sub-culturing adopted in water examination must be strictly followed, and the special tests for _Bacillus typhosus_ and _B. coli_ applied. As we have already seen, the quantitative estimation of organisms in milk is not of the same value as in water.