1889.] MICROSCOPICAL JOURNAL. 41 



BACTERIOLOGY.* 



Method of Preparing Nutritive Gelatine. — The following- 

 method is one of the best. Tubes to be used for the storing and subse- 

 quent inoculation of the gelatine must be thoroughly cleansed, dried, 

 plugged with cotton-wool or fine cotton, and sterilized. This is done 

 bv heating them for one hour in a hot-air sterilizer or oven at a temper- 

 ature of 150 C. (300 F.) 



Care should be taken that the plugs fit firmly, but not too tight. 

 When the tubes are ready the following method is recommended : 



Take, for example, 250 grams (about one-half pound) of good beef 

 after all fat has been removed. Chop or grind this to a fine pulpv mass. 

 Transfer it to a beaker, and add 500 c.cm. of distilled water — i. e., 

 2 c.cm. of water for every gram of chopped beef. Thoroughly stir up 

 the beef in the water, and then place it in an ice-box, or, if in winter. 

 in a cold room until the next day. 



On the following morning the meat infusion should be thoroughly 

 stirred, and the liquid portion separated by filtering and squeezing through 

 a linen cloth. The red liquid thus obtained must be brought up to the 

 amount of water taken on the previous day by adding distilled water. 

 To this is now added 1% of peptone, \% sodium chloride, and 10% of 

 the best gelatine. This would be in the case taken, 5 grams of peptone, 

 2.5 grams of salt, and 50 grams of gelatine. The beaker containing 

 this mixture is now placed in a water bath and heated to 45 C. and 

 allowed to stand for some minutes, until the gelatine is completely dis- 

 solved. 



The next process requires the greatest care and attention. Most 

 micro-organisms grow best in a slightly alkaline medium. This is ob- 

 tained by adding, drop by drop, a nearly saturated solution of sodium 

 carbonate to the beef-infusion-peptone gelatine mass until the reaction 

 is slightly alkaline, which is determined by its turning red litmus paper 

 to a faint blue. If by accident it should be made too alkaline it can be 

 neutralized by the addition of lactic acid. In order to clarify it the 

 white of two eggs is now added and thoroughly stirred into the gelatine 

 mixture. 



It is now boiled for one-half hour by placing the beaker or flask con- 

 taining it in a large water bath or covered kettle. After boiling it is 

 allowed to cool and set, after which it is again heated to the boiling 

 point, and filtered while hot. A hot filtering apparatus is necessary for 

 this. It may, however, be filtered with the ordinary filter in a hot-air 

 chamber at a temperature of 6o° C. The funnel should be kept covered 

 while filtering to avoid evaporation. 



The process of filtration must be repeated if necessary until the fil- 

 trate is perfectly clear. It is of a pale amber color generally, varying 

 in tint according to the amount of blood in the meat used. It is desir- 

 able to filter it into a sterilized narrow-necked flask to avoid evapora- 

 tion. It is now ready to be distributed in tubes. The sterilized test- 

 tubes are filled for about one-third of their depth (7 to 8 c.cm. in each) 

 by pouring in the gelatine carefully and steadily to prevent the mixture 

 from touching the part of the tube with which the plug comes in con- 



*This department is conducted by V. A. Moore, assistant in the laboratory of the Bureau of Animal 

 Industry. ■ 



