86 CLINICAL BACTERIOLOGY. 



divided into two equal parts with a knife sterilized in the 

 flame. The halves, resting upon sterile rubber rings, are 

 preserved in moist culture-chambers, whose individual 

 glass parts have been disinfected with mercuric chlorid. 



(/) Peptone-water. For the diagnosis of cholera a solu- 

 tion of one per cent, peptone and one per cent, sodium 

 chlorid in distilled water is required. This is rendered alka- 

 line, is sterilized for an hour in the steam-chamber, and is 

 kept in readiness in test-tubes, or, better, in so-called Pas- 

 teur flasks. The latter are closed by means of a glass 

 helmet drawn out into a tube, so that evaporation of the 

 water is prevented, and they provide a large surface of fluid 

 for the developing bacteria. 



For examinations of water, and also for the cultivation 

 of cholera -vibrios from water, a twenty-five per cent, solution 

 of peptone and of sodium chlorid is kept in readiness, and 

 is preserved in test-tubes, each of which contains four cubic 

 centimeters. If the contents of such a tube be added to 

 100 cu. cm. of the water to be examined, a one per cent, 

 solution of peptone and of sodium chlorid at once results, 

 which, after being rendered alkaline, is known as a fertiliz- 

 ing solution and can be used for culture-purposes. 



{g) Milk is likewise frequently used as a nutritive medium. 

 Fresh milk is introduced into test-tubes or into Erlenmeyer 

 flasks provided with cotton stoppers and sterilized. In 

 order to exclude bacteria the tubes and their contents are ex- 

 posed thrice for an hour each time, or once in the autoclave 

 at a temperature of 1 10 C. (230 F.) or 120 C. (248 F.). 



(/^) To determine the question whether a given variety 

 of bacteria produces acid or alkali in the course of its devel- 

 opment, the whey of Petruschky may be employed with 

 advantage. One liter of milk is added to a like amount of 

 water, and coagulation is effected by adding to the mixture 

 the smallest possible amount of acid (acetic acid). The 

 fluid is now filtered, and the filtrate neutralized with sodium 

 carbonate and heated to boiling. By this means the acid 

 reaction is, as a rule, restored, and turbidity results, which 

 is removed by filtration. Then the mixture is boiled again, 

 is neutralized with sterile sodium-carbonate solution, and 

 sterile tincture of litmus is added until a faint violet color 

 is produced. 



(i) Of less common culture-media, employed only for 

 special purposes, may be mentioned bread-pap (dry bread 



