BACILLUS TYPHOSUS. 427 



occurs nothing more is needed; the result is negative 

 as far as this specimen is concerned. If marked 

 clumping and immobilization of the bacilli immedi- 

 ately begin and become complete within five minutes, 

 this is denominated a marked immediate typhoid re- 

 action, and no further test is considered necessary, 

 though it is always advisable to confirm the reaction 

 with higher dilutions up to 1 to 20 and 1 to 50. If, 

 however, upon examination of the mixture there is no 

 marked immediate reaction, but the bacilli only show 

 in the first few minutes an inhibition in their motility 

 and a tendency to clump, which becomes more marked 

 but not complete within five minutes, this must be 

 tested with the higher dilution of 1 to 20, so as to 

 measure the exact strength of the reaction. If in the 

 1 to 20 dilution a complete reaction takes place within 

 thirty minutes, the blood is considered to have come 

 from a case of typhoid infection, while if a less com- 

 plete reaction occurs it is considered that a probability 

 only of typhoid infection has been established. The 

 time allowed for the development of the reaction with 

 the high dilutions is by many from one to two hours, 

 but to us thirty minutes seem safer. Positive results 

 obtained in this way may be taken to be conclusive 

 unless there be grounds for suspecting that the reaction 

 may be owing to a previous fairly recent attack. The 

 absence of reaction in one examination is considered 

 by us to in no way exclude typhoid infection. If the 

 case remains clinically doubtful, the examination should 

 be repeated within a few days. 



Proportion of Oases of Typhoid Fever in which a Defi- 

 nite Reaction Occurs and the Time of its Appearance. 

 As the result of a large number of cases examined in 



