110 



MICROSCOPIC METHODS 



condition into contact with the bacteria. The stages of pro- 

 cedure are the following : 



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 

 dry. The blood is drawn 

 up into a Wright's blood 

 capsule (Fig. 47) or into 

 the bulbous portion of a 

 capillary pipette, such as 

 in Fig. 46, a. (These pip- 

 ettes 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 pip- 

 ette. The serum is then 

 to be diluted. 



2. The serum may be 

 diluted (a) by means of a 

 graduated pipette either 

 a leucocytometer pipette 

 (Fig. 46, b] or some corre- 

 sponding form. In this 

 way successive dilutions 

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

 etc., can be rapidly made. 

 This is the best method. 



, (&) By means of a capillary 



\ / -i- n pipette with a mark on the 



tube, the serum is drawn 

 d 



FIG. 46. Tubes used in testing agglutinating and 

 sedimenting properties of serum. 



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 



