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



61 



broth, and the column of fluid which occupies it is allowed to run up 

 very gently, so as to avoid any back lash, into the bulb. The inflow 

 of air is arrested as soon as the capillary stem is empty of fluid. 



(a.) Method of Measuring off' and Mixing together equal Volumes of 

 Serum and Baetericd Cultures. 



The end of the capillary stem is now inserted into the narrow open 

 •end of the blood capsule, which has been placed ready to hand in a 

 perforated rubber bung or other convenient receptacle. The serum is 

 allowed to flow in until it reaches the pencil mark. 



The orifice of the pipette is now raised above the surface of the 

 .serum, and a bubble of air is admitted into the tube to serve as an 

 index for the next measurement. 



This done, the end of the capillary stem is carried over into a 

 watch-glass containing the particular dilution of the culture which is 

 to be dealt with in this particular tube. The culture is allowed to 

 flow in until the bubble of air has just been carried past the pencil 

 mark. 



The next procedure is to mix together the equal volumes of serum 

 and culture which have been measured off. This is effected by blow- 

 ing these two volumes out upon the surface of a sterile watch-glass — 

 a pile of inverted sterile watch-glasses will for this purpose have been 

 placed ready to hand — and drawing up and driving out the fluid 

 .several times in succession. After a little practice* this can be quite 

 easily achieved without driving the sterile broth down from the bulb 

 of the pipette into the lower part of the capillary stem and there con- 

 taminating it. 



The column of mixed serum and culture is to be drawn up into the 

 middle region of the capillary stem as a preliminary to sealing the 

 lower end of the tube. It will be found that when the column is left 

 in this position, the intervening column of air which occupies the 

 upper portion of the capillary tube will effectually isolate the fluid in 

 the bulb of the pipette for the mixture of serum and culture. 



The teat is now removed, leaving the spiral to guard the contents 

 of the tube against contamination, and the filling of the series of 

 tubes with the remaining dilutions of the culture is proceeded with. 

 When the whole series of tubes has been filled in, these are placed 

 upright in a test tube labelled with the date and the source of the 

 serum. The serum is then allowed to exert its influence on the 

 bacteria with which it has been brought in contact for a fixed period 

 at a fixed temperature. 



* Until practice shall have conferred sufficient control over the teat, it will be 

 advisable either to employ very fine capillary tubes or to provide a by-channel for 

 the air by piercing the teat -with a spicule of an extremely fine capillary tube. 



