TYPHOID FEVER 9 1 



for some time after complete convalescence from typhoid 

 fever; the reaction has been known to persist for seven or 

 eight years, and probably usually does so for about one or 

 two. This fact must be remembered in interpreting the 

 results obtained from Widal's test. If the patient has suffered 

 from typhoid fever, or from an obscure illness, which might 

 possibly have been typhoid fever, a year or two previously, 

 the positive reaction should be regarded with suspicion. 



In such cases the test should be carried out so that the 

 smallest dilution which will cause clumping can be ascertained, 

 and the test repeated in two or three days. If, for instance, 

 we found that the blood clumps only in a dilution of i in 20 

 on one day, and in a dilution of i in 100 three days later, this 

 affords a certain proof that the reaction is due to a present 

 attack of typhoid fever, and is not due to one which took place 

 at a previous date. This investigation should be entrusted 

 to an expert bacteriologist, and plenty of blood sent on each 

 occasion. 



3. Typhoid carriers are persons who, after passing through 

 an attack of typhoid fever, excrete typhoid bacilli in their 

 urine or faeces, or both, for various periods of time. Such 

 patients are a constant source of dang'er to those brought in 

 contact with them, and have been known to start many 

 epidemics. They usually give a marked Widal reaction for 

 more prolonged periods than do ordinary typhoid convales- 

 cents, and this fact may afford a clue to their recognition, for 

 which an examination of the urine and faeces must be made. 



4. That the patient has recently been inoculated against 

 typhoid. 



A negative result may mean : 



1. That the patient is not suffering- from typhoid fever. 



2. That he is suffering from typhoid fever, but the date is 

 too early for the appearance of the reaction. The reaction 

 sometimes occurs on the fifth or sixth day, usually by the 

 tenth day, and in all but a very small number of cases before 

 the end of the second week. If the onset of the disease (as 

 far as it can be fixed) is less than this, the examination should 

 be repeated after two or three days. (With the method given 

 subsequently (Dreyer's), agglutination can be determined 

 before these dates.) 



3. In a very small number of cases the reaction is delayed 



