36 



CLINICAL BACTERIOLOGY AND HEMATOLOGY 



examine the serum for some time seal the other end to prevent 

 evaporation. 



When the blood has coagulated it will begin to contract away 



Fig. i6 



from the sides of the tube, the serum being forced out of the clot. 

 When this process is complete there will be a central dark- 

 coloured clot suspended in clear serum. The tube can now be 



Fig. 17. 



notched with a file and broken, and the serum removed with a 

 pipette and used for Widal's reaction, the estimation of the 

 opsonic index, etc. If much serum is required, the pipette can 

 be hung by its crook (straight end downward) in the bucket of a 



