128 PA TJ1OGEN1C BACTERIA. will. It is prepared as follows : To 1000 c.cin. of meat- infusion or to 1000 e.cni. of water containing 2 grains of beef-extract in solution, 10 grams of peptone, 5 grams of salt, and 100 grams of gelatin (uGolcl label" is the best commercial article) are added, and boiled for about an hour over a moderately hot flame. Double boilers are very slow, and if proper care is exercised there is little danger of the gelatin burning. It must be stirred occa- sionally, and the flame should be so distributed by wire gauze as not to act upon a single point of the bottom of the kettle. At the end of the hour the albumins of the meat-infusion will be coagulated and the gelatin thoroughly dissolved. Giinther has shown that the gelatin congeals better if allowed to dissolve slowly in warm water before boiling. The liquid is now cooled to 60° C. and neutralized—/. e. alkalinized. As the gela- tin is itself acid, a relatively larger amount of the sodium- carbonate solution will be needed than was required for the bouillon. When the proper reaction is attained, as much water as has been lost by vaporization during the process of boiling, intimately mixed with the white of an egg, is added, well stirred in, and the whole boiled for half an hour, then filtered. If the filter-paper be of good quality and properly folded (pharmaceutical filter), and if the gelatin be prop- erly dissolved, the whole quantity should pass through before cooling too much. Should only half go through before cooling, the remainder must be returned to the pot, heated to boiling once more, and then passed through a new filter-paper. As a matter of fact, gelatin generally filters readily. A wise precaution is to catch the first few centimeters in a test-tube and boil them, so that if a cloudiness shows the presence of uncoagulated albumin, the whole mass can be boiled again. The finished gel- atin is at once distributed into sterilized tubes, and then sterilized like the bouillon by the fractional method. Of course, the gelatin or any other culture-medium can be kept en masse indefinitely, but should a contaminating"