408 APPENDIX II 



filtered and sterilised. 3. An accurately neutralised solution con- 

 taining 4 . 5 per cent sodium citrate, 1 . 5 per cent sodium chloride, 

 and 0.225 per cent atropine sulphate. 4. A 5-per-cent solution 

 of sodium bicarbonate. In a test-tube mix one cubic centimetre 

 of the diluted stain, two cubic centimetres of the citrate solution, 

 and three cubic centimetres of the molten agar solution. To 

 this mixture a quantity of the alkaline sodium bicarbonate 

 solution must be added in order to cause the excitant for leucocytes 

 contained in the jelly to diffuse into the cells, and the quantity 

 added varies with the temperature of the room. 1 If measurements 

 are going to be made in a room with a temperature of between 

 60 and 70 F., about . 25 cubic centimetre of the alkaline solution 

 should be added. The mixture is then boiled until it froths up 

 the tube and a drop poured on to a slide and allowed to set so as to 

 form a film. Supposing a given capillary tube contains the blood- 

 corpuscles of one person mixed with the plasma of another, the 

 average number of living and dead leucocytes in the tube can be 

 estimated by placing a drop of its contents on a cover-glass which 

 is inverted and allowed to fall on the agar film. After two or 

 three minutes the granules but not the nuclei of the living leuco- 

 cytes will stain and those cells will show exaggerated amoeboid 

 movements, whereas the dead cells will remain immobile. More- 

 over, the dead cells may be achromatic (3), in which case they will 

 not stain. Their nuclei may appear as a single nuclear mass, 

 or their nuclei may even stain, or the dead cells may have under- 

 gone other changes which have been described in former papers 

 (1, 2). Field after field should be rapidly passed in front of 

 a l-6th inch or equivalent objective and the number of the 

 living and dead cells counted. Several preparations can be rapidly 

 examined and an average struck so as to give an estimate of the 

 number of living and dead cells in the given capillary tube. No 

 difficulty is met with in making the counts, for living can be 

 readily differentiated from dead cells by the presence or absence of 

 exaggerated movements . 



If all the leucocytes appear to be dead, and especially if the 

 agar jelly has not previously been tested, it is as well to control 

 1 A scale has been given in the former paper. 



