190 A MANUAL OF BACTERIOLOGY 



they will, in fact, grow and multiply in an agglutinating 

 serum. The amount of agglutination does not bear any 

 constant ratio to the intensity of an infection ; on the 

 whole, if the patient is reacting satisfactorily to an infec- 

 tion, the agglutination reaction tends to be marked ; if 

 not, it may be feeble or absent. Thus, in severe typhoid 

 infections with fatal issue, agglutination may be absent. 

 RufEer and Crendiropoulo * regard the agglutinins as 

 being formed in the polymorphonuclear leucocytes. 



The Agglutination Reaction 



A. For Clinical Diagnosis (" Widal " Reaction) 



This is principally made use of in typhoid and paratyphoid fevers, 

 Malta fever, and bacillary dysentery. 



Collection of blood. Blood is collected (p. 214), preferably in a 

 Wright's capsule (Fig. 35, d, p. 215), or in a capillary bulbous pipette 

 (Fig. 7, p. 52), or in a vaccine tube. The ends of the tube are sealed, 

 the dry end always being sealed first ; the blood is allowed to 

 coagulate (which may be hastened by placing in the blood-heat 

 incubator), and then centrifuged to separate the serum, care 

 being taken that the dry sealed end of the tube, which will be 

 perfectly sealed, is distal when spinning. 



If tubes are not available, the blood may be spotted on to a 

 piece of glass, cover-glass, or slide, glazed paper, tinfoil, etc., and 

 allowed to dry. For use, a drop of distilled water is placed on the 

 dry blood to dissolve it, and the solution used like serum. 



The culture. For the microscopic test a young broth culture is 

 to be preferred. A hanging drop should be examined to ascertain 

 that clumps are absent ; this specimen is kept as a control. If 

 clumps are present they may be removed (in the case of typhoid) 

 by filtering the culture through filter-paper. A suspension of an 

 agar culture may also be used, likewise dead cultures : a broth 

 culture or suspension of an agar one being heated to 65 C. for ten 

 minutes and preserved in sterilised glass pipettes ; dead cultures 

 are, however, unsatisfactory in tropical climates. For the macro- 

 scopic test a thick suspension of an agar culture in salt solution is 

 to be preferred, the suspension being allowed to sediment for half 



1 Brit. Med. Journ., 1902, vol. i, p. 821 (Bibliog.). 



