Should we wish to examine a drop of milk for bacteria, we proceed in this manner. With the aid of the Cornet’s forceps pick up two cover slips, place a drop of milk on one and cover with the other. With thumb and finger bring the glasses into close contact, so that the milk forms a thin film. Slide one glass from the other and set aside, milk side upwards, till dry. Next take each cover slip, separately, in the forceps and pass rapidly two or three times through the flame of a spirit lamp, this fixes the bacteria, if any be present, to the glass. Now having poured a little of the stain, say methylene blue, into a shallow vessel, a saucer will do, we place our cover slips therein for two minutes or so. Then, remove them with the forceps, wash in water till no more stain comes away and set aside to dry. When dry, take a clean slide, place a small drop of Canada Balsam at its centre and gently lower the cover slip thereon, stained side downwards. If we now examine our slide under a high magnification, we shall easily be able to see whether bacteria are present or not. Should our preparation be too deeply stained, a good slide will show the bacteria stained blue against an almost colourless background, we must immerse our second preparation for a few moments in a little of the 1/2 per cent. acetic acid which will have the effect of removing the excess of stain; then, after washing and drying, we proceed as before. Beautiful double staining may be performed by the following method. In addition to the chemicals we already possess we shall require some 5 per cent. acetic acid. Double staining is especially useful for spore-forming bacteria, so we may take some of the Hay Bacillus at sporing time. Proceed exactly as described above substituting, of course, a drop of water known to contain the bacilli for the drop of milk. When the two cover slips are ready for staining, warm some of the Carbol-Fuchsin in a saucer and leave the cover slip therein for five minutes, then transfer to a 5 per cent. solution of Acetic Acid till all the stain appears to be removed, afterwards wash in water. The cover slips must next be immersed for a few minutes, two should be long enough, in Methylene blue solution, then washed and, when dry, mounted on a slide with Canada Balsam, as described above. If the staining has been properly carried out, we shall have a most beautiful preparation, showing spores stained red and the rest of the bacilli blue.