374 TYPHOID FEVEK 



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 occuivin 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 due to other intestinal infections. 



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 cany out the test for himself. For this the standard 

 cultures (p. 118) are used. 



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 

 degree by the urine. The blood of a fcetus may have little 

 agglutinating effect, though that of its mother may have given 

 a well-marked reaction ; sometimes, however, the total blood 

 gives a well-marked reaction. It may here also be mentioned 

 that a serum will stand exposure for an hour at 58° C. without 

 having, its agglutinating power much diminished. 'Higher 

 temperatures, however, cause the property to be lost. It is 

 sometimes necessary to heat the serum to 55° C. for thirty 

 minutes before testing for agglutination as bacteriolytic sub- 

 stances may be present ; such heating destroys the complement 

 concerned in the lytic action (see Chapter IV.). 



With regard to the value of the serum reaction there is little 

 doubt. In nearly 95 per cent, of cases of typhoid it can be 

 obtained in such a form that no difficulty is experienced if the 

 precautions detailed above are observed. The causes of possible 

 error may be summarised as follows : The serum of the person 



