84 CLINICAL BACTERIOLOGY AND HiEMATOLOGY 



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 bacilH in their urine or 

 faeces, or both, for long periods of time. Such patients are a 

 constant source of danger 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 convalescents, and this fact may afford a 

 clue to their recognition, for which a trained bacteriologist 

 should be consulted. 



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 con- 

 valescence in mild attacks, but this is exceedingly rare. 



4. Paratyphoid fever is a comparatively rare disease, clinically 

 like typhoid fever, but due to organisms presenting minute differ- 

 ences in their chemical properties. Patients infected with these 

 organisms do not clump the ordinary typhoid bacilli, but give the 

 reaction when tested with the appropriate culture. This should 

 be borne in mind, and cases which appear to be typhoid clinically 

 should be tested with cultures of paratyphoid bacilli. 



Vaccine Treatment. — Antityphoid vaccines are used in the treat- 

 ment of the developed disease, and also as preventive agents. 

 Their curative use has not fully established itself as a practical 

 method, though very good results have been claimed. Small 

 doses only are used. For prophylaxis a dose of 500 millions 

 followed by 1,000 millions after ten days or a fortnight, are given, 

 or, I think preferably, three doses of 250, 500, and 1,000 millions 



