384 TYPHOID FEVER 



be delayed, but it may be incomplete, the clumps formed being 

 small and many bacilli being left free. These latter may either 

 have been rendered motionless or they may still be motile. No 

 diagnosis is conclusive which is founded on the occurrence of 

 such an incomplete clumping alone. Seeing that low dilutions 

 sometimes give a reaction with non-typhoid sera, it is important 

 to know what is the highest dilution at which complete 

 clumping indicates a positive reaction. The general consensus 

 of opinion, with which our own experience agrees, is that when 

 a serum in a dilution of 1 : 30 causes complete clumping in half 

 an hour, it may safely be said that it has been derived from a 

 case of typhoid fever. Suspicion should be entertained as to 

 the diagnosis if a lower dilution, or if a longer time is required. 



The reaction given by the serum in typhoid fever usually 

 begins to be observed about the seventh day of the disease, 

 though occasionally it has been found as early as the fifth day, 

 and sometimes it does not appear till the third week or later. 

 Usually it becomes gradually more marked as the disease 

 advances, and it is still given by the blood of convalescents from 

 typhoid, but cases occur in which it may permanently disappear 

 before convalescence sets in. How long it lasts after the end of 

 the disease has not yet been fully determined, but in many cases 

 it has been found after several months or longer. As a rule, up 

 to a certain point, the reaction is more marked where the fever 

 is of a pronounced character, whilst in the milder cases it is less 

 pronounced. In certain grave cases, however, the reaction has 

 been found to be feeble or almost absent. In some cases, which 

 from the clinical symptoms were almost certainly typhoid, the 

 reaction has apparently been found to be absent. Such cases 

 should always be investigated, from the point of view of their 

 possibly being paratyphoid fever. 



It has been found that the reaction is not only obtained with 

 living bacilli, but in certain circumstances also with bacilli 

 that have been killed by heating at 60 C. for an hour, if a 

 higher temperature be used, sensitiveness to agglutination is 

 impaired. Dreyer has introduced a simple technique which 

 enables an ordinary practitioner provided with dead cultures to 

 carry out the test for himself. The capacity is also still retained 

 if a germicide be employed. Here Widal recommends the 

 addition of one drop of formalin to 150 drops of culture. The 

 reaction, however, tends to be less complete. 



Besides the blood serum, it has been found that the reaction 

 is given in cases of typhoid fever by pericardial and pleural 

 effusions, by the bile and by the milk, and also to a slight 



