TESTING OF PROPERTIES OF SERUM. 



119 



sedimentation is shown by the formation within a given 

 time (say 12 or 24 hours) of a somewhat flocculent layer 

 at the bottom, the 

 fluid above being 

 clear. Two points 

 should be attended 

 to. Controls should 

 always be made 

 with normal serum, 

 and the serum to 

 be tested should 

 never be brought 

 in the undiluted 

 condition into con- 

 tact with the bac- 

 teria. The stages 

 of procedure are 

 the following : 



i. Blood is con- 

 veniently obtained by 

 pricking the lobe of 

 the ear, which should 

 previously have been 

 washed with a mixture 

 of alcohol and ether 

 and allowed to dry. 

 The blood is drawn up 

 into the bulbous por- 

 tion of a capillary 

 pipette, such as in 

 Fig. 41, a. (These 

 pipettes can be readily 

 made by drawing out 

 cmill glass tubing in 

 a flame. It is con- 

 venient always to have 

 several ready for use. ) 

 The pipette is kept in the upright position, one end being closed. For 

 purposes of transit, break off the bulb at the constriction and seal the 

 ends. After the serum has separated from the coagulum the bulb is 

 broken through near its upper end and the serum removed by means of 

 another capillary pipette. The serum is then to be diluted. 



FlG. 41. Tubes used in testing agglutinating 

 and sedimenting properties of serum. 



