AGGLUTININS 7S 



members of the same group of bacteria, such as B, 

 typhosus, and B, paratyphosus A and B, though not 

 with the same intensity. Members of this group can 

 be differentiated by using different dilutions of the 

 agglutinating serum, the specific organism involved 

 being agglutinated by the greatest dilution of serum. 

 Agglutination tests are occasionally employed in the 

 diagnosis of glanders, cholera, Malta fever, and in 

 staphylococcus and streptococcus infections. 



The Widal Reaction 



The agglutination test for the diagnosis of typhoid 

 fever is known generally as the Widal reaction, be- 

 cause this investigator, though by no means the dis- 

 coverer of the method, first used it extensively in 

 clinical work. 



There are two methods of carrying out the test: 

 microscopically and macroscopically. Of these, the 

 microscopic method is that more generally employed. 



A. MICROSCOPIC METHOD 



For the performance of the test we require blood- 

 serum from the suspected patient, and a recent culture 

 of typhoid bacilli. 



The description of the test may therefore be 

 divided into three portions, viz.: {a) collection and 

 dilution of the patient's blood-serum; (b) prepara- 



