262 A MANUAL OF BACTERIOLOGY 



serum. There will now be in the pipette (counting from the 

 nipple towards the point) one volume of bacterial suspension, a 

 bubble of air, a volume of leucocytes, a bubble of air, and lastly a 

 volume of serum (c, Fig. 36). 



Now express the contents of the pipette into a small watch- 

 glass, or hollow-slide, or artist's sunk palette, and mix well to- 

 gether, aspirating them repeatedly into the pipette and expelling 

 without causing bubbles. If bubbles form, a hot wire brought 

 near will quickly dispel them. When thoroughly mixed, aspirate 

 the mixture into the pipette, suck up a short volume of air, and 

 seal the tip in the flame. 



Then place the pipette point downwards in the incubator, or 

 better, in a water-bath at 35 to 37 C., noting the time exactly, 

 and proceed to prepare a second pipette in precisely the same 

 way, using the same suspensions of bacteria and leucocytes, but 

 the control serum instead of the patient's. Place this in the incu- 

 bator or water-bath, by the side of the other, noting the time at 

 which this is done. When a pipette has been incubated for a 

 quarter of an hour it is removed from the incubator or water- 

 bath, the end broken off and the teat fitted to the thick end ; 

 then the contents are expelled on to a hollow slide or porcelain 

 palette and mixed thoroughly together. Films are then pre- 

 pared. This may be done by depositing a drop in the middle of 

 a large cover-glass (1-in. squares, No. 2), dropping on to it another 

 cover-glass and drawing the two apart. Or the films may be 

 made on slides, for which Wright recommends roughing the slides 

 with finest emery paper and spreading the film with the sharp edge 

 of a broken slide (see below). The films are then stained. For 

 staphylococci, streptococci, pneumococci, B. coli, etc., the films 

 may be fixed with formalin and stained with carbol-thionine blue 

 or borax-methylene blue (see " Malaria "), or they may be stained 

 without previous fixing with the Leishman stain. For tubercle, 

 the films may be fixed in a saturated solution of mercuric chloride 

 (one or two minutes), stained in warm carbol fuchsin, decolorised 

 with 2| per cent, sulphuric acid in methylated spirit, and counter- 

 stained with methylene blue (Plate I, a and &). 



Wright now uses the whole blood instead of the leucocyte layer 

 only. After the blood has been drawn into the citrated salt solu- 

 tion it is centrifuged, washed twice with salt solution, the fluid 

 is pipetted off, and finally the corpuscles are well mixed. The 



