204 METHODS OF SERO-DIAGNOSIS. 



The substances in the serum producing this action on the bacteria 

 they named agglutinins, since they differed from the lysins, inas- 

 much as they resisted the effects of heating at 55° C, and when 

 the agglutinating effect was destroyed by the effects of higher 

 temperature, it could not be restored by the addition of the 

 complement present in fresh serum. 



It was Widal and Grunbaum who, in 1896, showed that this 

 phenomenon could be made use of in a practical manner to 

 demonstrate the presence of agglutinins in the serum of patients 

 in the early stages of typhoid fever. We shall see later how the 

 agglutination test is applied in practice, but before leaving this 

 part of the subject, we may examine the action of these agglu- 

 tinins a little further. 



It was, later, found, that these agglutinins could be called 

 into existence by the injection of many other varieties of bacteria 

 than those mentioned (the quantities produced varying with the 

 particular species used"), and even by the use of red corpuscles, 

 the bodies formed in this latter case being known as hsemaglu- 

 tinins. The agglutinins are relatively thermostable, resisting, as 

 before noted, the effect of a temperature of 55° C, and some even 

 withstanding heating to 65 — 70 ° C. The reaction between the 

 substance (agglutinogen) giving rise to the agglutinating bodies, 

 and these latter was explained by Ehrlich, according to his side- 

 chain theory, by assuming that the agglutinin was composed of 

 two molecule groups, one of which is haptophore. combining with 

 the body, agglutinated, this action being brought about by the 

 other molecule group of the agglutinin. There is much evidence, 

 however, in support of the view that the reaction is of a chemico- 

 physical nature ; and Rordet, who showed that the presence of 

 sodium chloride was necessary for the occurrence of the reaction, 

 holds the idea that it can be explained by assuming that the 

 surface tension of the I'quid, in which the combined agglutinating 

 and agglutinable substances are suspended, acting on this com- 

 plex, brings the particles together, when, in obedience to gravity, 

 they settle to the bottom of the liquid. There are many who 

 consider that the action of agglutinins is directlv comparable with 

 that of the next class of antibodies to be considered. 



The Precipitins. — These were first described by Kraus in 

 1897, who found that the serum, derived from animals immunized 

 against the organisms of plague, cholera and typhoid fever could., 

 when added to the filtered fluid in which cultures of these organ- 

 isms had been growing, produce a precipitate in the liquid. 



Observations in this direction being extended, it was found 

 that this reaction could be induced by the serum of animals 

 immunized against other kinds of albuminous material, when their 

 serum was added to solutions of these materials, such as blood- 

 serum, milk, muscle-extracts and albuminous urine, to mention 

 only a few substances used for this purpose. Thus the test came 

 to have a great diagnostic value, not so much, however, in the 

 realms of bacteriology as in those of human forensic medicine 

 and also the inspection of meat, where the "precipitin method" 



