CULTIVATION OF BACTERIA. 197 



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 2^ per 

 cent, solution of the alkali-albuminate with 1 per cent, of 

 peptone, 1 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 : l 



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 

 adding a few drops of clean water to each tube before 

 sterilizing. It is not necessary to have a special small 

 chamber blown in the tube to contain this water; only 



1 The Medical News, vol. L, 1887, p. 138. 



