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



results of bacterial enumerations carried out at a series of successive 

 intervals upon one and the same mixture of serum and culture. The 

 fallacy just referred to comes in in connection with the circumstance 

 that all evidence of a bactericidal effect exerted will be obliter- 

 ated if the intervals between the successive enumerations happen 

 to be such as to allow of the covering up of losses due to the bacteri- 

 cidal action of the serum by a subsequent multiplication of the 

 surviving micro-organisms. 



A further point which has been kept in view in designing the above 

 method, is the importance of obtaining a simple numerical expression 

 for the bactericidal power of the blood. 



Such a simple numerical expression is obtained by specifying the 

 number of bacteria contained in 1 c.c. of the lowest dilution of the 

 bacterial culture which is completely sterilised by digestion with an 

 equal volume of serum. 



While a convenient basis for the comparison of the bactericidal 

 power of a series of different bloods is thus provided, it must be under- 

 stood that the expression just referred to is nothing more than an 

 arbitrary formula expressing the bactericidal effect of the serum 

 brought into application in the form of a 50 per cent, solution. 



If it is desired in any case to determine the bactericidal effect exerted 

 by the serum in a practically undiluted condition, this can readily be 

 achieved by making a graduated series of dilutions of the enumerated 

 culture, using the serum itself as a diluent. 



In concluding this section it will perhaps not be amiss to point out 

 that the method of bactericidal estimation here described may be 

 employed not only for determining the bactericidal power of the blood,, 

 but also for determining that of any chemical antiseptic. 



Section II. — Method of Measuring the Bactericidal Power of the Blood 

 under Anaerobic Conditions. 



The method of measuring the bactericidal power of the blood under 

 anaerobic conditions which is here to be described, is similar to the 

 method described in the previous section, except in so far as the 

 technique is modified with a view to excluding the air from contact 

 with the blood. 



Access of air is prevented by enveloping the blood in oil. 



It is essential that this oil should be absolutely neutral, first, because 

 the presence of fatty acid might affect the bactericidal power of the 

 serum by diminishing its alkalinity and by precipitating its calcium 

 salts, and, secondly, because an oil containing fatty acids is emulsified 

 when it is brought in contact with serum, nutrient broth, and alkaline 

 fluids generally. Such an emulsification would interfere with that 

 sharp separation of the oil from the enclosed fluids which is absolutely 



