120 



METHODS OF EXAMINING SERUM 



contact with the bacteria. 

 following : 



The stages of procedure are the 



I 



1. Blood is conveniently obtained by pricking the lobe of the ear, 

 which should previously have been washed with a mixture of alcohol 



and ether, and allowed to 



s- dry. The blood is drawn 



up into a Wright's blood- 

 capsule (Fig. 45) or into 

 the hollow bulbous portion 

 of a capillary pipette, such 

 as in Fig. 44, a. (These 

 pipettes can be readily 

 made by drawing out quill 

 glass -tubing in a flame. 

 It is convenient 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. 



2. The serurn may be 

 diluted (a) by means of a 

 graduated pipette either 

 a leucocytometer pipette 

 (Fig. 44, &) or some cor- 

 responding form. In this 

 way successive dilutions 

 of 1 : 10, 1 : 20, 1 : 100, 

 etc., can be rapidly made. 

 This is the best method. 

 (b) By means of a capillary 

 pipette with a mark on the 

 tube, the serum is drawn 

 up to the mark and then 

 blown out into a glass 

 capsule ; equal quantities 

 of bouillon are successively 

 measured in the same way, and added till the requisite dilution is 

 obtained, (c) By means of a platinum needle with a loop at the end 

 (Delepine's method). A loopful of serum is placed on a slide, and the 

 desired number of similar loopfuls of bouillon are separately placed 

 around on the slide. The drops are then mixed. 



A very convenient and rapid method of combining the steps 1 and 2 



-a- k 



FIG. 44. Tubes used in testing agglutinating 

 and sedimenting properties of serum. 



