428 BACTERIOLOGY. 



the health department laboratories, it has been found 

 that about 20 per cent, gave positive results in the first 

 week, about 60 per cent, in the second week, about 80 

 per cent, in the third week, about 90 per cent, in the 

 fourth week, and about 75 per cent, in the second 

 month of the disease. In 88 per cent, of the cases in 

 which repeated examinations were made (hospital cases) 

 a definite typhoid reaction was present at some time 

 during the illness. 



Persistence of the Reaction. This peculiar property 

 of the blood-serum may persist in persons who have 

 recovered from typhoid fever for a number of months. 

 Thus a definite typhoid reaction has been reported in 

 serum from three months to a year, and a slight reac- 

 tion, though much less than sufficient to establish a 

 diagnosis of typhoid infection, from one to fifteen 

 years, after convalescence from the disease. 



The Reaction with the Blood-serum of Healthy Persons 

 and of Those III with Diseases other than Typhoid Fever. 

 An immediate marked reaction has not been observed 

 in a 1 to 10 dilution of the blood-serum of over one 

 hundred healthy persons examined in the health depart- 

 ment laboratories. In several hundred cases of diseases, 

 not believed by the physicians in charge to be at the 

 end of the disease typhoid fever, only very rarely did 

 the serum give a marked immediate reaction in a 1 to 

 10 dilution, and here in the light of past experience, I 

 believe a typhoid infection, though not a typical typhoid 

 fever, to have existed. These results have been con- 

 firmed by others, the question of dilution having been 

 recently made the subject of elaborate investigations, 

 with the view of determining, if possible, at what 

 dilution the typhoid serum would react and others 



