94 BACTERIOLOGICAL DIAGNOSIS. 



of one in a hundred three days later, this affords a cer- 

 tain 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 en- 

 trusted to an expert bacteriologist and plenty of blood 

 sent on each occasion. 



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 after 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. 



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

 delayed still further, and if the patient dies may not 

 occur at all. These cases are usually severe ones and 

 do not present any difficulty in diagnosis. Sometimes 

 the reaction is delayed well into the convalescence in 

 mild attacks, but this is exceedingly rare. 



MACROSCOPIC METHOD. 



The macroscopic method can be carried out with a 

 young living culture on agar, or with an emulsion of 

 dead bacilli. The technique is not so difficult as in the 

 previous process and no apparatus is required other 

 than a piece of narrow glass tubing from which to make 

 pipettes. 



Requisites. i. A young culture on agar and some 



