386 EXPERIMENTAL INFECTIONS DURING LIFE 



Mount these two cover-slips on a double-celled slide. 



2 . Note the time : Examine the control to determine 

 that the bacilli are motile and uniformly scattered over 

 the field not collected into masses. 



3. Next examine the 50 per cent, serum preparation. 

 If agglutinin is present and the test is giving a 



positive reaction, the bacilli will be collected in large 

 clumps. 



If the test is giving a negative reaction, the bacilli 

 may be collected in large clumps owing to the viscosity 

 of the concentrated serum. 



4. Observe the 5 per cent, preparation microscopic- 

 ally. 



If the bacilli are aggregated into clumps, positive 

 reaction. 



If the bacilli are not aggregated into clumps, observe 

 until thirty minutes from the time of preparation before 

 recording a negative reaction. 



5. Examine the 0.5 and 0.05 per cent, preparations. 

 These may or may not show agglutination when the 



result of the examination of the 5 per cent, preparation 

 is positive, according to the potency of the specific 

 serum ; and by the examination of a series of dilutions 

 a quantitative comparison of the valency of specific 

 sera from different sources, or of serum from the same 

 animal at different periods during the course of active 

 immunisation may be obtained. 



NOTE. The graduated pipettes supplied with Thoma's haema- 

 tocytometer (intended for the collection of the specimen of blood 

 required for the enumeration of leucocytes), giving a dilution of 

 i in 10 i. e., 10 per cent. may be substituted for the graduated 

 capillary pipettes referred to above, if the vessel in which the 

 serum has been separated is of sufficiently large diameter to per- 

 mit of their use. 



The Macroscopical Reaction : 



Sterile graduated capillary pipettes to contain 90 c. mm. 

 Eighteen to twenty-four-hours-old bouillon cultivation of the 

 organism to be tested. 



