i66 



PRACTICAL METHODS IN IMMUNITY 



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, Malta 

 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. 



Even in a small laboratory there are no particular difficulties in the way of having 

 on hand rabbits immunized against typhoid, paratyphoid, Malta fever, acid- 

 producing and nonacid-producing strains of dysentery, cholera, etc. Just as we 

 inject men with vaccines prepared from various bacteria in opsonic therapy, so we 

 inject animals to produce sera for diagnosis. We may use either a bouillon culture 

 or the growth on agar slants taken up with salt solution as the inoculating material. 

 This is heated for one hour at 6oC. to kill the bacteria. Where we desire to produce 

 a serum which will disintegrate red blood cells (hiemolytic serum), we inject intra- 

 venously about i c.c. or intraperitoneally about 5 c.c. of the washed red cells of the 

 animal for which we wish to produce a specific serum. For details see method of 

 preparing haemolytic amboceptor serum under Noguchi's modification of Wassermann 

 test. 



Precipitating Sera. For preparing a serum for the biological blood test we inject 

 the rabbit intravenously with human serum in quantities of about 5 c.c. every fifth 

 day. About one week after the last injection the antiserum obtained from the in- 

 jected rabbit should be strong enough for Ho c.c. to produce turbidity when added 



