PREPARATION OF THE SERA 113 



the tubercle bacillus as short a variety of the organism as 

 possible should be selected, and a mass of growth off a solid 

 medium is taken (bacilli in mass can be obtained in the market 

 from wholesale chemists) and is well washed with changes of 

 distilled water, dried on filter paper in a Petri dish and 

 thoroughly rubbed up with a little 1*5 per cent saline in an 

 agate mortar so as to disintegrate the bacterial masses and 

 get an emulsion composed as far as possible of individual bacilli. 

 This must be controlled by microscopic examination. A thick 

 cream should be obtained, and this should be sterilised by 

 steaming for half an hour on three successive days. Before 

 sterilisation it is convenient to seal up the stock emulsion -in 

 small quantities in a number of pieces of quill tubing so that in 

 the subsequent procedures only small portions of the emulsion 

 are exposed to aerial contamination at one time. For actual 

 use, one of those tubes is opened, a little is withdrawn with a 

 sterile pipette, and a weak emulsion made in the same way as 

 with the staphylococcus except that 1'5 per cent saline is used. 

 The stock tube may be sealed with wax and kept for use again. 

 A fresh emulsion ought to be made up for each day's work. 



(2) Preparation of leucocytes. Here the observer uses his 

 own blood cells. A 1*5 per cent solution of sodium citrate in 

 85 per cent sodium chloride is prepared. This is placed in a 

 glass tube three inches long made by drawing out a piece of 

 half-inch tubing to a point, the tube being filled nearly to the 

 brim. A handkerchief being bound round the finger, this is 

 now pricked and the blood allowed to flow directly into the 

 fluid, to the bottom of which it sinks. The tube ought to be 

 inverted between the addition of every few drops of blood so as 

 to bring the blood in contact with the citrate and prevent 

 coagulation. The equivalent of about ten to twenty drops of 

 blood should be obtained. The diluted blood is then centri- 

 fugalised, and when the corpuscles are separated the super- 

 natant fluid is removed, '85 per cent saline is substituted and 

 the centrifugalisation repeated. The fluid is again removed, 

 care being taken not to disturb the layer of white cells lying on 

 the top of the red corpuscles. This layer is then pipetted off 

 into a watch-glass or tube and the leucocytes required are thus 

 obtained. 



(3) Preparation of the sera. The serum whose sensitising 

 effect on the bacteria it is desired to test is obtained by Wright 

 as follows. A " blood capsule " is made by drawing a piece of 

 No. 3 quill tubing into the shape shown in Fig. 47, the part not 

 drawn out being about one inch in length. It is convenient to 



