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-serwm of Healthy Persons 
and of Those Ill with Diseases other than Typhoid Fever. 
An immediate marked reaction has not been observed 
in a1 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 
