THE COLON-TYPHOID GROUP 141 



dilutions of the serum have been recommended (i : 50), and 

 this should be used in cases of doubt. So far, about 95 per 

 cent, of the cases examined, and which clinically were con- 

 sidered typhoid fever, have given a positive reaction. It is 

 not often present until the fifth day of the fever, and dis- 

 appears usually within a year, though in some individuals it 

 has been found ten years after an attack of the disease. 



The agglutinating properties have been found in nearly all 

 the secretions of the body tears, urine, milk, pleuritic effu- 

 sions serous fluid from blisters, etc. 



Fig. 61. The Widai agglutination reaction (Slater and Spitta). 



There is no relation between the reaction and the bacteri- 

 cidal power of the serum; the agglutination is not a destruc- 

 tion. The agglutinating power is active, though the blood be 

 dried and sealed up for months. It seems to have no direct 

 relation with the question of immunity, since it occurs at the 

 height of the disease, and intense agglutinating serum may 

 be had in severe cases and in cases with relapses. A negative 

 result does not exclude typhoid. 



The test is quantitative i. e., it depends upon the dilution 

 of the blood-serum, since the serum of healthy persons in 

 strong dilution will cause agglutination and loss of motility. 



