149 
The second specimen of urine from J. K. was obtained four days 
after the first. No treatment had been given the boy in the mean- 
while, and yet the typhoid organism, neither at the second nor at 
subsequent examinations, was found. 
If these three positive results are accepted, several interesting con- 
siderations present themselves: 
(a) These three persons are chronic typhoid bacillus carriers. 
The fact that the bacillus was not found in any of the specimens 
after the first for each case may have been due to all three of these 
‘‘carriers’’ having been in periods, known, to occur with bacillus 
carriers, w^hen the excreta are apparentl}^ free from the organism. 
It seems to us, however, that it is improbable that all three of the 
persons were chronic carriers, in view of the fact that all specimens 
after the first ones gave negative results. 
(b) That these three persons were temporary bacillus carriers and 
perhaps harbored the bacilli for but a few days or weeks. That 
they did not have the disease may have been due to the absence of 
other factors concerned in the etiology of typhoid infection. Still, if 
they are viewed as temporary carriers, which in face of the evidence 
seems more reasonable than the view that they are chronic carriers, 
we must admit that, if there are in the District of Columbia about 
900 persons during the typhoid season who without having typhoid 
fever clinically do discharge typhoid bacilli, if only for a few days, 
they must be considered as important factors m the spread of infection. 
(c) The finding of t}q)hoid bacilli in the feces of two or three 
healthy persons per 1,000 of population in a community may have 
diminished significance in the epidemiology of t^q^hoid fever. If 
these organisms do not cause disease of the hosts in whose intestinal 
canals theq^ are found, it is evident that other factors are necessary 
in the etiology of typhoid fever. 
This is following the view suggested by Pettenkofer, that the 
causation of tjqihoid fever may be represented by XYZ In this 
combination the typhoid bacillus is X, and unless Y and Z are also 
operative, disease does not result. 
In this connection it is interesting to consider the possibility of 
typhoid bacilli being harbored as harmless parasites in the intestinal 
canal, gall bladder, hepatic ducts, or elsewhere in the human body 
for months or even years and then, by having added the other (YZ) 
elements of the etiologic complex, produce the disease. 
The possibility in some cases of a long period of time elapsing 
between the time of taking the bacilli into the body and the onset 
of the disease must be considered, even if the typhoid bacillus is 
looked upon as the sole cause of the disease, specific susceptibility 
to this organism being the only other factor concerned. Accepting 
this hypothesis, it is conceivable that typhoid bacilli, like tubercle 
