128 BACTERIOLOGY OF MEAT AND MEAT PRODUCTS 



bacteria generally is desired it will be necessary to make dilu- 

 tions. An accurate enumeration cannot be made since all the 

 bacteria cannot be brought into the watery emulsion obtained 

 from the solid meat, but comparable results can be obtained as 

 follows: select the piece for examination, cut it up as finely 

 as possible with sterile instruments and introduce 2 grammes 

 (weighing in on a balance) into a bottle with glass or india- 

 rubber stopper containing 20 c.c. of sterile water. After thorough 

 mixing various quantities of the emulsion are used for examina- 

 tion, diluted fractions being obtained in the usual way. 



For purposes of calculation it is assumed that the organisms 

 in the meat are all contained, after mixing, in the sterile water 

 and the results are recorded as per gramme of material. 



To detect bacteria and study the varieties present the usual 

 plan is to make linear cultivations on tubes or plates of sterile 

 media with small fragments removed from the meat or organs 

 under examination. The bacteria which grow are then studied 

 in detail. 



Conradi's enrichment method mentioned above is a more 

 certain method of detecting any bacilli present, but is somewhat 

 complicated for routine work. It is briefly as follows : imme- 

 diately after the animal has been slaughtered a piece weighing 

 about 50 grammes of the organ to be examined is removed 

 with sterilized knife and forceps and then placed for four hours 

 either in 2 per cent, corrosive sublimate at 37 C. or, if it is to 

 be forwarded to the laboratory, in 0*2 per cent, sublimate. On 

 its reception at the laboratory the organ is placed in a large 

 sterilized conical glass with overlapping cover, which can be 

 hermetically sealed by resin-wax. It remains in this sterile 

 moist chamber at 37 C. for a further period of 12 16 hours. 

 The piece is then divided into two. The centre of one half is 

 plunged into fluid nutrient gelatine and kept at 37 C. to develop 

 anaerobic bacilli. The other half is smeared over the surface of 

 sterile plates, those selected by Conradi being, in order, a brilliant 

 green picric acid plate, a plate of Drigalski-Conradi medium 

 and a plate of nutrient agar. Finally a hanging-drop cultiva- 

 tion and a microscopic specimen stained by Gram's method are 

 made. This method is also used for Gaertner group bacilli. 



