68 LABORATORY COURSE IN SERUM STUDY 



the killed typhoid suspension to each tube and incubate as in the first 

 experiment. It should be noted that the sensitiveness of the immune 

 bodies to heat varies somewhat according to the dilution in which they 

 are exposed, and if desired, exposure to 56 C. may be repeated with un- 

 diluted serum. 



The student is referred to the literature given in the text-book on 

 the work of Joos and others on the variation in heat stability of agglu- 

 tinins according to whether they are produced by the injection of heated 

 or unheated bacteria. 



LESSON X 



AGGLUTININS (Continued) 

 I. AGGLUTINATION BY MICROSCOPIC METHOD 

 (WIDAL TEST) 



DILUTIONS for the microscopic test may be made in the same 

 manner as those for the macroscopic, but it is often desirable in 

 clinical tests to work with smaller amounts of serum than can be 

 measured accurately in the ordinary graduated pipettes. In this 

 case capillary pipettes are used and the serum is measured either 

 by counting drops of serum and of salt solution, the same pipette 

 held at the same angle being used for both to insure accuracy, 

 or by using as an arbitrary unit the amount of fluid contained in 

 a capillary pipette from the tip to a wax pencil mark placed about 

 an inch from the tip. Students should practice making dilu- 

 tions by both of these methods. The former is the usual method 

 employed in diagnostic work ; the latter, however, is more ac- 

 curate. 



Reagents : 



1. Serum of rabbit immunized to B. typhosus. 



2. B. typhosus 24 hour culture in broth. 



3. Salt solution. 



Take four watch glasses or saltcellars and by means of a capillary 

 pipette provided with a rubber nipple place 9 drops of salt solution in the 

 first watch glass and 5 drops in each of the other three. With the same 

 pipette place one drop of serum in the first saltcellar; (if a highly 



