SERUM DIAGNOSIS 141 



the injection of the antimicrobic serum (passive immunization) has been 

 thought by some to be of value. When we allow a mixture of bac- 

 teria or cells to remain in contact with their specific immune serum 

 which has been inactivated, the amboceptors attach themselves to the 

 bacteria or cells, so that now, upon adding normal serum (comple- 

 ment), these bacteria or cells are so prepared 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 applications 

 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 organism which is suspected 

 as the cause of the disease. The Widal test (agglutination) is the best instance of 

 this procedure. This method is of practical value in the diagnosis only of typhoid, 

 Maltg, fever, and para-typhoid. 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 suf- 

 fered from a suspected disease. Thus, by testing the agglutinating power of a serum, 

 one or two weeks after recovery 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. Organisms isolated from urine, 

 faeces, or blood of patients, or those obtained from water or food supplies may be 

 identified by testing the agglutinating, 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 information than do agglutina- 

 tion or bacteriolytic tests. With the majority of other organisms, however, the 

 agglutination test is the one almost always preferred. 



