180 APPLIED BACTERIOLOGY 



the ends as not to become heated. It is preferable for the 

 capillary tubes to be sterile, in case of its being impossible 

 to examine the blood soon after collection ; but it is not 

 essential if the interval does not exceed a few hours. It is 

 best if the tube can be centrifugalised so as to obtain a 

 clear serum ; if this cannot be done, it will be found that, 

 after a few hours, on breaking off the ends of the tube (and 

 in the case of a V-tube, in the middle also), a string of clot 

 and some serum can be blown out on to a glass slide, and 

 the serum with some corpuscles collected in another capil- 

 lary tube, or in the diluting pipette to be described imme- 

 diately. If the tube has been centrifugalised it is broken 

 off at the junction of serum and corpuscles, and the clear 

 serum blown out. 



A diluting pipette is easily made from a small capillary 

 tube with a small bulb, with the aid of the graduated 

 pipettes of a haemocytometer. These are graduated for 

 5 c.mm. and 20 c.mm. ; a mark is made on the diluting 

 pipette at 5 cmm. and 80 cmm., so that we can dilute the 

 serum in the proportion of 1 to 16. This is done by 

 sucking the serum from the glass slide up to the first mark, 

 and then bouillon or "6 per cent. NaCl solution after it up 

 to the second mark, blowing the whole out again on to the 

 glass slide and thoroughly mixing. It is well to suck up 

 and blow out two or three times to ensure thorough 

 mixing. 



If a diluting pipette is not available, the following 

 method as recommended by Del^pine may be adopted. 

 Fifteen drops of broth or salt solution are successively taken 

 up in a loop of platinum wire, and placed on a glass slide ; 

 close to them is placed one drop of the serum, and the 

 sixteen drops are then thoroughly mixed. 



A small drop of this diluted serum has then to be mixed 

 on a cover-glass with an equal-sized drop of a broth culture 



