98 



LABORATORY EXERCISES IN BACTERIOLOGY. 



the openings in the cover of the jar and swept about the sides of the interior so as 

 to break the clot away from the glass, and thus permit its complete shrinkage. The 

 wire is then withdrawn and the opening closed with its cotton plug. Thereafter the 

 jar should be transferred to the laboratory with as little disturbance of its contents 

 as possible and placed in the refrigerator for twenty-four to forty-eight hours for 

 thorough separation of the serum from the clot. In the mean time a series of large 

 test-tubes or narrow flasks of suitable size are arranged for receiving the serum and 

 sedimentation of the blood-cells which are apt to be transferred with it (Fig. 28). In 

 such a series of sedimentation tubes the connecting glass tubes are set into double- 

 perforated rubber stoppers. All the parts are first well cleaned, the stoppers loosely 



FIG. 29. BLOOD TUBE WITH SIPHON ARRANGED TO TRANSFER SERUM FROM JAR TO 

 SEDIMENTATION TUBES ; TUBE a TO BE KEPT ABOVE LEVEL OF SERUM IN LAST 

 TUBE. 



applied, and the series folded together in compact manner and sterilized in the 

 autoclave. On removal from the autoclave the stoppers are at once firmly adjusted 

 and the series of tubes placed upon supports made of blocks of wood with suitable 

 holes bored into them. A sterilized rubber tube is now inserted through one of the 

 openings in the jar, well down into the serum overlying the clot, and connected with 

 the first tube of the series. After this connection is made a second rubber tube is 

 connected with the escape of the last of the series to serve as a mouthpiece, and strong 

 suction made to start siphonage into the test-tubes. If the apparatus has been ar- 

 ranged with the jar considerably higher than the series of tubes, the siphonage 

 will without difficulty carry the serum from one tube to another in the series and 

 nearly fill all (Fig. 29). 



