MACROSCOPIC METHOD. 95 



normal saline solution ; or a dead emulsion of typhoid 

 bacilli. 



2. Special glass pipettes. These are to be made from 

 a piece of glass tubing which should not be more than 

 J in. in internal diameter and about ten inches long. 

 The central two inches of this tube are to be heated in 

 a flat gas flame until thoroughly softened, then with- 

 drawn, and then the two ends are to be drawn steadily 

 apart. The softened portion is to be drawn out into 

 a long narrow portion (rather thicker than a vaccine 

 tube) about six inches long and of nearly uniform dia- 

 meter. The full diameter of the tube should pass vapidly 

 into this narrow portion ; it should not taper gradually 

 (fig. 12, c}. The two pipettes thus obtained are to be 

 broken apart, leaving about three inches of the narrow 

 tubing attached to each. The wide end of the tube is 

 to be plugged fairly firmly with cotton-wool. This 

 serves a double purpose ; it prevents any of the fluid 

 from getting into the mouth, and it offers a certain 

 amount of resistance to the escape of the fluid, and thus 

 renders the pipettes more easy to fill. 



Process. Prepare an emulsion just as before, making 

 a drachm or so, and filtering it. An emulsion of dead 

 bacilli obtained from a laboratory should be ready for 

 immediate use. Insert the tip of the pipette into the 

 blood serum (of which there should be several drops), 

 and aspirate it gently into the tube, avoiding air- 

 bubbles ; if these gain access blow out the serum and 

 begin again. It is easier to see what you are doing 

 if you use a piece of india-rubber tubing (such as is 

 used with a haemocytometer) through which to apply 

 suction. 



Having drawn up enough serum to form a column 

 about two inches in length in the narrow portion of the 



