380 



IMMUNOLOGY 



(twenty-foiir-liour Ijrotli cultures or saline suspensions washed 

 from a twenty-four-hour agar slant) or dead suspensions pre- 

 served with formalin were quite satisfactory for use in the test. 



The suspensions should be' diluted to match a satisfactory 

 turbidity standard and tested for agglutinability by serums of 

 known potency. The importance of flagellar and somatic antigenic 

 factors is discussed later in this chapter. It is quite important that 

 a smooth motile strain be used in antigen preparation. 



Two Techniques Employed. — There are two methods employed 

 to determine whether the patient's serum will agglutinate at a di- 



71 



Twbe 

 Result 



V 



ViJ s^ ^^ v2/ 



'0 



Mom,al R„.b« Pot,enti ^al.ne, PoS.k.ve 



M ^ I 1. ^ 1 ,'^°"i,'o' Widal Reaction 



Modtjq. Complete Cor.<plete No 

 a^^ aqq. aa(j 



Fig. 1.5. — Positive Widal test. 



agnostic titer suspension of E. tyyhosa. One is the macroscopic 

 while the other is the microscopic technique. The former is usually 

 the method of choice and the diagnostic titer used is as a rule 

 1-80. In carrying out the macroscopic Widal, one adds a uniform 

 and measured amount of bacterial suspension to each of four 

 vials or small test tubes. One then adds equivalent amounts of 

 1 :40 dilution of normal human serum to the first, of 1 :40 dilution 

 of known positive human serum to the second, 1 :40 dilution of 

 patient's serum to the third, and saline to the fourth tube. This 

 is indicated in Figs. 15 and 16. Where the agglutinability of the 



