136 BACTERIOLOGY FOR NURSES 



The opsonic index as a guide for the administration of vaccine 

 was at one time considered its most practical use. Observation 

 showed that following an injection of vaccine the opsonins were 

 decreased for a longer or shorter period, the so-called negative 

 phase, and that later an increase occurred, the positive phase. 

 The purpose of recording the opsonic index was so to determine 

 the dose and the time of administering the vaccine that the nega- 

 tive phase should be as limited as possible. The opsonic index 

 is much less used at present in vaccine therapy; it requires a 

 considerable amount of time to determine and can only be relied 

 upon when undertaken by skilled workers. 



Agglutinins. According to Ehrlich's side chain theory agglu- 

 tinins are antibodies of the second order. They possess like 

 antitoxins and lysins a portion for uniting with their antigens. 

 They also possess zymophore portions to which their special reac- 

 tion is due. Metchnikoff believed that the agglutinins are derived 

 from the leukocytes and endothelial cells. It is generally thought, 

 however, that the bone marrow and the spleen are most active 

 in their formation. 



If the serum of a patient suffering from typhoid fever is added 

 to an emulsion of typhoid bacilli, and the mixture placed in the 

 incubator for a short period, the bacteria which were formerly 

 scattered throughout the fluid will be found to have clumped 

 together in small masses at the sides of the test tube, and as they 

 gradually fall to the bottom the fluid becomes clear. If a hang- 

 ing drop preparation is made it will be observed that with the 

 addition of serum the bacilli move closer together, gradually losing 

 their motility, until finally they adhere in clumps. 



In 1896 Widal applied this fact to the diagnosis of typhoid 

 fever, and since agglutinins appear comparatively early in the 

 disease it is a considerable aid both in typhoid fever and in other 

 diseases in which agglutinins are formed. The test may be made 

 macroscopically by sedimentation of the clumps in a test tube 

 or microscopically in a hanging drop ; the latter method is best 

 adapted for diagnostic purposes when a quick report is necessary 

 and only a small amount of serum is available. 



