FORMATION OF AGGLUTININS 



281 



independent of Widal, but, owing to a lack of patients, Widal preceded 

 him in the publication of a more extensive work. 



At the present time this diagnostic reaction is known as the Gruber- 

 Widal reaction. It has proved of great value to a large number of dif- 

 ferent investigators, not only in making the serum diagnosis of typhoid 

 fever, but in other infections as well. 



Normal and Immune Agglutinins. Normal serums are frequently 

 capable of agglutinating bacteria, such as the typhoid, colon, pyocy- 

 aneus, and dysentery bacilli. In some cases the typhoid bacillus may be 

 agglutinated in dilutions as high as 1 : 30, a point of practical impor- 

 tance in the clinical use of the test. When a normal serum is found to 

 have a high agglutinating power, it is probable that 

 a previous infection by the microorganism has oc- 

 curred. Since the serum of a new-born child is 

 largely devoid of agglutinins that are found in later 

 life, the so-called normal agglutinins may, after all, 

 be acquired properties. 



The term immune agglutinin is applied to the 

 agglutinating substance in a serum developed as the 

 result of infection or of systematic immunization 

 with the microorganism. 



Formation of Agglutinins. According to Ehr- 

 lich's side-chain theory, agglutinins are antibodies of 

 the second order (Fig. 78). They resemble antitoxins 

 or receptors of the first order in possessing an affinity- 

 bearing or haptophore group that unites with the 

 antigen, but they differ from them in having also a 

 functional or agglutinophore group that agglutinates 

 the antigen when this union has occurred (Fig. 79). 



Agglutinins that have lost their zymophore or agglutinophore group 

 through the action of heat, age, acids, etc., but that still possess their 

 haptophore group, are called agglutinoids, just as toxins that have lost 

 their toxophore group are called toxoids. Such agglutinoids, then, may 

 still combine with the bacteria or blood-cells without being able, how- 

 ever, to produce agglutination (Fig. 80). 



It is found, at times, that even a fresh serum, when concentrated, 

 will cause less agglutination than when it is diluted. This is ascribed to 



presence of agglutinoids, which have a stronger affinity for agglutin- 



m than has the agglutinin. When producing a reaction of this char- 

 acter they are called pro-aqglutinoids. When the serum is diluted, the 



79. THEO- 

 RETIC STRUC- 

 TURE OF AGGLU- 

 TININ AND AG- 

 GLUTINOID. 



1, Agglutinin: 

 H, Haptophore 

 group for union 

 with antigen; A , the 

 agglutinophore or 

 zymophore group. 



2, Agglutinoid. 

 Same structure as 

 agglutinin, except 

 that the agglutino- 

 phore or zymophore 

 group is lost. 



