TECHNIC OF BACTERIOLYTIC TESTS 349 



If granule formation occurs in the first two or three animals, but is 

 absent in the culture control, the reaction may be regarded as positive, 

 and the diagnosis of typhoid, cholera, etc., considered as established. 



If granule formation occurs to any extent in the fifth animal (culture 

 control), the culture is to be regarded as unsuitable and the test repeated. 



Measuring the Bactericidal Power of the Blood in vitro by the Plate 

 Culture Method (Stern and Korte). Since the earliest days of bac- 

 teriology the aim and purpose have been to devise some means by which 

 the bactericidal power of the blood could be measured, just as is done in 

 testing an ordinary germicidal substance, namely, by adding a bacterial 

 suspension to the serum and observing the effect on the bacterial con- 

 tent. This is shown by counting the bacteria in a loopful immediately 

 after adding the bacterial suspension, and repeating this at regular in- 

 tervals, the counting being done by the method of plate culture. 



The use of the platinum loop in these tests is objectionable, since the 

 dose is quite variable, depending upon whether the loopful is removed 

 from the fluid edgewise, or with the loop held flat, like a spoon in use. 

 If the serum contains agglutinins, the results with any form of technic 

 are likely to be irregular, and the number of colonies upon the plate stand 

 in no relation to the actual number of microorganisms present. The 

 results may be masked by a rapid multiplication of the survivors, and 

 accordingly several controls are necessary with any technic. 



Neisser and Wechsberg have recommended the so-called bactericidal 

 plate culture method. By this method the patient's serum is inactivated, 

 and varying amounts mixed with definite and constant quantities of 

 bacteria. To this a constant quantity of active normal serum is added 

 as complement, to reactivate the bacteriolytic amboceptors. These 

 mixtures are then incubated for several hours. To determine whether 

 and in what proportion death of bacteria has resulted from the effect of 

 the bacteriolysins, agar is added, and the mixtures are then plated and 

 incubated for twenty-four hours or longer. The number of colonies are 

 then counted and the results compared with control plates of the culture 

 alone. 



Stern and Korte have modified this technic slightly, and recommend 

 the procedure as a substitute for the Pfeiffer test in the clinical diagnosis 

 of typhoid fever. The method spares a certain number of animals, but 

 it is somewhat more complicated than the Pfeiffer reaction, and its re- 

 sults are less trustworthy. As a clinical test, therefore, it is to be recom- 

 mended only in cases in which the agglutination reactions have yielded 

 uncertain results, although with practice and care the test oftentimes 



