124 PRACTICAL METHODS IN IMMUNITY. 



pared that the complement can disintegrate them. This experiment 

 is termed " sensitizing" and cells so treated are said to be "sensitized." 



METHODS FOR OBTAINING IMMUNE SERA. 



While a convalescent from a disease may be utilized to obtain an 

 antitoxic, agglutinating, opsonic or bacteriolytic serum against the 

 specific bacterium, yet this is more conveniently obtained from an 

 animal which has been immunized against the bacterium or cell in 

 question. The rabbit is the most convenient animal to employ for the 

 production of immune sera where the object is to have at hand a serum 

 for use in diagnosis. 



Where sera are used on an extensive scale, as in the production of 

 curative sera, larger animals are employed. There are two application 

 of serum diagnosis : i . Where the bacterium is known and the serum 

 is to be diagnosed. 2. Where the serum is known and the bacterium 

 is to be diagnosed. 



The first is employed by testing the agglutinating or bacteriolytic 

 power of the serum taken from a patient upon pure cultures of the organ- 

 ism which is suspected as the cause of the disease. The Widal test (ag- 

 glutination) is the best instance of this procedure. This method is 

 of practical value in the diagnosis only of typhoid, Malta fever and 

 paratyphoid. In diseases like cholera and bacillary dysentery, the 

 disease has run its course before agglutinating power becomes apparent 

 in the serum. This method, however, may be used to prove that 

 a convalescent has suffered from a suspected disease. Thus, by test- 

 ing the agglutinating power of a serum, one or two weeks after re- 

 covery from a suspicious case of ptomaine poisoning, we may be able 

 to demonstrate that the case in question was cholera. The second 

 method has wider application, and is the one in which we use the sera 

 of animals which have been immunized with known bacteria. Or- 

 ganisms isolated from urine, faeces or blood of patients, or those obtained 

 from water or food supplies may be identified by testing the agglu- 

 tinating, opsonic or bacteriolytic power of known sera against them. 

 This has a wide range of applicability. The testing of the opsonic 

 power of the sera in man or animals immunized against plague, and 

 possibly cerebrospinal meningitis, seems to give more definite informa- 



