236 A MANUAL OF BACTERIOLOGY 



like minute white flakes in a clear fluid. In a strongly agglu- 

 tinating blood this takes place in the lower dilutions almost 

 instantaneously after the agglutinometer slide begins to revolve. 

 The change is very striking, and can be easily seen with the naked 

 eye. In the higher dilutions the change may take three or four 

 minutes, and be observable only with the aid of a pocket lens. If 

 no change is visible with the pocket lens in the 1 in 10 dilution at 

 the end of five minutes' time limit, no agglutinin of any diagnostic 

 significance is present in the blood. 



The agglutinin titre of the serum is the highest dilution in which 

 definite flakes of agglutinated bacilli can be seen with the aid of a 

 pocket tens. It is essential that the dilution beyond this be abso- 

 lutely negative if it be desired to ascertain the limit of agglutina- 

 tion. In this case, should the highest primary dilution of serum 

 prepared (1 in 320) show agglutination, higher dilutions may be 

 prepared and tested. 



(The apparatus may be obtained from the Engineer, London 

 Fever Hospital, Liverpool Eoad, Islington, London, N.) 



5. B or det- Durham reaction. This is carried out by any of the 

 foregoing methods in much the same manner as for clinical diag- 

 nosis, but an immune serum of high agglutinating value or high 

 "titre" (at least 1: 1,000) is required, and the serum from a 

 patient is not usually suitable. The immune serum may be 

 obtained from a horse or other animal immunised with killed 

 cultures (and living also if a high titre is required). In the 

 laboratory the serum may be prepared by giving a rabbit three 

 to five intravenous injections at intervals of seven days of killed 

 culture of a virulent strain of the organism, e.g. typhoid or cholera. 

 The culture is killed by heating to 60-65 C. for half an hour, and 

 the dose is increased from one loop to ten loops of an agar culture. 

 Seven days after the last dose the animal is bled from an ear vein, 

 and the serum obtained. The agglutinating limit of the serum 

 must be determined, and dilutions towards this limit used in the 

 test, e.g. if the limit be 1-1,000, dilutions of 1-500 and 1-750 

 might be employed. Controls should be put up with a known 

 culture. Controls should also be put up with normal serum of 

 an animal of the same species as that from which the immune 

 serum has been obtained. 



6. Saturation test. Ten loopfuls of a young agar culture of the 

 organism to be tested are mixed with 10 c.c. of a 5 per cent, dilu- 



