74 CLINICAL BACTERIOLOGY AND 



The emulsion-tube should now be scratched at its narrow 

 end with the glass-knife and broken off, but before doing 

 so it is well to sterilize the end in the flame. A ligature 

 should now be placed round one's finger, and the finger 

 pricked; with the pipette one unit volume of blood 

 should be taken up. Then a column of air, one volume 

 of emulsion, another column of air, and one volume 

 of diluent (i.e., a £ per cent, citrate of soda in a 

 normal saline solution). If the emulsion is very thick, 

 several volumes of diluent may be taken up. This latter 

 prevents the blood coagulating. The teat of the pipette 

 should now be pressed, and the contents expelled on to a 

 clean slide, taken up again and expelled until a thorough 

 mixing has taken place. As soon as the test-tube containing 

 the emulsion is finished with, it should be sealed in the flame 

 and set aside for sterilization. Three slides should now be 

 laid in front of the operator; these slides should have 

 their surfaces roughened by rubbing with emery-paper 

 (Hubert's 00), and a drop of the mixture placed on a corner 

 of each slide, on their convex surface spread out with the 

 spreader, and allowed to air dry. They are then placed in 

 a trough to fix, containing a saturated solution of corrosive 

 sublimate; washed thoroughly under the tap, and stained 

 with filtered carbol-thionin for two minutes ; washed again, 

 and dried with filter-paper. The specimen is now ready 

 for examination, and should show, if satisfactory, a 

 fairly even field of bacteria, with blood -cells. More- 

 over, the bacteria should not be in bundles or chains. 

 If they are, the emulsion must be well shaken again; or 

 if there is a great dearth of bacteria, we must make 

 a stronger emulsion, or, rather, add a smaller volume of 

 diluent, and go over the whole process as before, and make 

 fresh specimens. Should we, however, have a satisfactory 

 field (the beginner may have many unsatisfactory fields 

 before he gets a satisfactory one), we proceed to count the 

 bacteria and the blood-cells under a -^ oil-immersion lens 

 and the highest available eyepieces, so as to limit the field 



