134 PATHOGENIC BACTERIA. is filtered off and pure hydrochloric acid carefully added while a precipitate forms. The precipitated albuminate is collected upon a cloth filter, mixed with a small quan- tity of liquid, and made distinctly alkaline. To make solutions of it of definite strength it can be dried, pul- verized, and redissolved. The most useful formula used by Deycke was a 21/> per cent, solution of the alkali-albuininate with i per cent, of peptone, i per cent, of NaCl, and gelatin or agar-agar enough to make it solid. Potatoes.—Without taking time to review the old method of boiling potatoes, opening them with sterile knives, and protecting them in the moist chamber, or the much more easily conducted method of Esmarch in which the slices of potato are sterilized in the small dishes in which they are afterward kept and used, we will at once pass to what seems the most simple and satisfactory method of using this valuable medium—that of Bolton and Globig i1 With the aid of a cork-borer a little smaller in diam- eter than the test-tube ordinarily used a number of cyl- inders are cut from potatoes. Rather large potatoes should be used, the cylinders being cut transversely, so that a number, each about an inch and a half in length, can be cut from one potato. The skin is removed from the cylinders by cutting off the ends, after which each cylinder is cut in two by an oblique incision, so as to leave a broad, flat surface. The half-cylinders are placed each in a test-tube previously sterilized, and then are exposed three times, for half an hour each, to the pass- ing steam of the sterilizer. This steaming cooks the potato and also sterilizes it. Such cultures are apt to deteriorate rapidly, first by turning very dark; second, by drying so as to be useless. Abbott has shown that if the cut cylinders be allowed to stand for twelve hours in running water before being dispensed in the tubes, they do not turn dark. Drying may be prevented by 1 The Medical News, vol. 1., 1887, p. 138.