306 AGGLUTININS 



At each stage of the procedure the pipet is carefully washed and 

 dried out with successive quantities of absolute alcohol followed by 

 successive quantities of ether. 



Shake each tube thoroughly in order from right to left, i. e., beginning 

 each row with the highest dilution. 



Place the stain for two hours in a water-bath at 50 to 55 C. (not 

 in dry air). 



In Tube 1 of each row the serum acts in a dilution of 1 in 25. 

 In Tube 2 of each row the serum acts in a dilution of 1 in 50. 

 In Tube 3 of each row the serum acts in a dilution of 1 in 125. 

 In Tube 4 of each row the serum acts in a dilution of 1 in 250. 



Tube 5 containing no serum is control against spontaneous agglutination. 



If the limit of agglutination is not reached within this series, higher 

 dilutions are followed out in a similar manner. 



Thus, for example, 57 drops of normal saline solution plus 3 drops of 

 a 1 in 10 serum dilution will give a serum dilution of 1 in 200, and, using 

 the same quantities as before, one has the serum acting in dilutions 

 of 1 in 500, 1 in 1000, 1 in 2500, and 1 in 5000. And similarly for higher 

 dilutions. 



The tubes are examined, after two hours at 50 to 55 C., followed by 

 fifteen minutes' standing at room temperature. The reading is taken by 

 comparing each tube in succession with the control tube, and is pref- 

 erably made by means of artificial light against a black background. 

 If daylight is used, the tubes inspected should.be partly shadowed by 

 passing a finger up and down behind them. 



In non-inoculated persons who have not had typhoid (or paratyphoid) 

 fever, agglutination in a dilution of 1 in 25 justifies a strong suspicion 

 of typhoid (or paratyphoid) infection. Rut the test must be applied 

 again in the course of a few days to ascertain whether there is any change 

 in the titer of agglutination. Marked agglutination in a dilution of 

 1 in 50 or more is (nearly always) diagnostic of active typhoid (or 

 paratyphoid) infection. 



A non-inoculated carrier will normally show no important change 

 in the titer of his serum on repeated examination at short intervals. 



Inoculated persons if quite recently inoculated will usually show a 

 high titer of specific agglutination. A rapid rise in titer sets in within 

 two to four days of inoculation. This is followed by a fall at first rapid, 

 but subsequently becoming very slow, so that a relatively high titer is 

 maintained for a long period (even for years) . During this period ex- 

 aminations made at intervals of a few days give practically identical 

 readings. 



