58 



LABORATORY COURSE IN SERUM STUDY 



that is, the failure of the antibodies to act if present in excessive 

 concentration. In the sera of artificially immunized animals or of 

 typhoid patients amounts greater than 0.01 c.c. of a strongly im- 

 mune serum are usually ineffective, the best results being obtained 

 with amounts varying from 0.001 to 0.0001 c.c. in a volume of 1 c.c. 



Since the inactivated immune serum must, of course, be re- 

 activated by fresh normal serum used as complement or alexin, 

 it is important to use an amount of the normal serum too small to 

 be of itself bactericidal ; and the first step to determine is the 

 bactericidal power of the normal serum against the strain of 

 bacteria to be used. On the other hand, to secure striking results 

 it is necessary to use as large an amount of fresh normal serum 

 as possible without entering the zone of normal bactericidal 

 power. Normal rabbit serum is usually definitely bactericidal 

 for typhoid bacilli in amounts ranging from 0.1 to 0.02 c.c. (in a 

 total volume of 1 c.c.). 



Reagents : 



1. Anti-typhoid serum serum of a rabbit immunized against 

 typhoid bacilli obtained in sterile condition and heated at 56 C. for half 

 an hour. 



2. Normal rabbit serum, which must also be sterile. 



3. 24-hour broth culture of typhoid bacilli. 



The glassware and salt solution used in the experiment must, of 

 course, be sterile, and the reagents handled with care to avoid contam- 

 ination during the setting up of the experiment. 



TENTATIVE SCHEDULE l 

 Set up the following tubes: 





1 By a previous test of the serum the instructor should adjust the schedule so 

 that one or two tubes lie within the "killing " zone and others above and below it. 



2 The serum in this control tube should be that amount which shows maximum 

 bactericidal power when used with active serum. 



