3 2 4 TYPHOID FEVFR. 



serum can be blown out. To make the proper dilution, 

 a clean cover-glass is taken, and on this are placed at 

 separate points nine drops of the bouillon containing 

 the bacilli. These drops are conveniently measured by 

 a small platinum loop. At another point on the cover-glass 

 a similar drop of the blood or serum is placed, and the 

 mixture is then made. In this way the serum is diluted in 

 the proportion of i : 10. The drop is then placed on a 

 slide and examined under the microscope. 



We may mention another method which we have found 

 very convenient, but which requires a glass pipette, by 

 which a dilution is made of i : 10. (We use a leucocyto- 

 meter pipette for this purpose.) The blood is drawn up to 

 the mark i and bouillon is sucked after it up to the mark 

 n, the mixing being then effected in the bulb by shaking 

 from side to side. The mixture is then blown into 

 U-shaped tube of bore about an eighth of an inch, th< 

 length of the limbs being about three inches. Such 

 tube is very easily made by taking a piece of quill glass tube 

 about six inches in length, carefully heating the centre in a 

 Bunsen flame, and then bending till the two halves are 

 parallel to one another. (Many such tubes can be rapidl, 

 made at one time.) The U-shaped tube containing th 

 mixture is then centrifugalised. The result is that all the 

 corpuscles are collected in a thick mass at the bend, the 

 limbs of the tube containing a clear fluid composed, o 

 course, of the diluted serum. The diluted blood can be 

 used without separating the red corpuscles, but it i 

 preferable that this should be done. If a centrifuge i 

 not available, a considerable amount of separation ma) 

 be obtained by allowing the tube to stand in the vertica 

 position for a couple of hours. A small quantity of th 

 diluted serum is taken by means of a narrow glass pipette an< 

 placed on a slide, a slide with hollow cell being preferable 

 (vide Fig. 25, B). To this is added about half its quantity o 

 the bouillon containing the bacilli, and the two drops 

 mixed together. The cover-glass is then placed in posi 

 tion, and the specimen is examined, By this method the 



