1902.] the Bactericidal Power of small Samples of Blood. 59 



sufficient blood has been collected, the upper portion of the capsule is 

 gently warmed and the upper orifice is then immediately sealed up. 

 As the air, which has been rarefied by warming, contracts, the blood 

 is drawn up into the body of the capsule, leaving the orifice at (B) 

 free for resealing. After the capsule has cooled, it is suspended by 

 means of its curved arm in a hand centrifuge, and the blood is driven 

 down by a few turns of the handle into a previously upper half of the 

 capsule. It is now left at rest for a few minutes. When the serum 

 begins to exude, the centrifuge is again brought into action. 



When the estimation is to be taken in hand, the neck of the curved 

 bulb of the capsule is sterilised in the flame and is cut across with a 

 stout pair of bone forceps, which has been sterilised in the same 

 manner. 



Two further points in connection with sample of blood may appro- 

 priately be considered. The first of these relates to the question of 

 the necessity for aseptic precautions in drawing off the blood. The 

 second to the question of the interval which may elapse between the 

 drawing off of the blood and the bactericidal estimation. 



The blood should be drawn off with aseptic precautions. For this 

 purpose the surface of the finger may be readily and effectually 

 sterilised by moistening it with alcohol, and burning this off. 



Where results which are comparable among themselves are desired, 

 the bactericidal estimations ought, in all cases, to be undertaken 

 within a very few hours after the samples of blood have been with- 

 drawn. Where samples of blood are tested immediately after with- 

 drawal, and again after an interval of 24 hours, it is usual to find a 

 notable diminution of bactericidal power in the second estimation. 



(2.) Preparation of a Series of Graduated Dilutions of the 

 Bacterial Culture. 



It has already been indicated, but it will be well at this point clearly 

 to bring out the fact, that in the method of bactericidal estimation here 

 described, a series of measured volumes of undiluted serum are brought 

 in contact with a series of graduated dilutions of the culture, the 

 object being to determine what is the lowest dilution of the culture 

 with which a complete bactericidal effect is exerted. 



The graduated dilutions of the culture which are required for this 

 purpose, so far as they have not already been provided by the procedure 

 undertaken in connection with the enumeration of the bacterial culture, 

 would, at this stage, be prepared by the aid of the diluting pipette. I 

 have found it convenient in the case of the typhoid bacillus to employ, 

 in addition to the undiluted culture, in each case a 2 fold, 5 fold, 

 10 fold, 25 fold, 50 fold, 100 fold, 1000 fold, 10,000 fold, and 100,000 

 fold dilution. 



