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not a single secondary case develops among other persons in the 
household, or even in the neighborhood. In other instances, one or 
more cases are being cared for in a household in good sanitary sur- 
roundings, ordinary care as to cleanliness, disposal of patients’ ex- 
creta, personal contact with patients, etc., being exercised, and yet 
two or three or more secondary cases develop among other persons in 
the house or in houses near by. 
Of course in making a comparison of such instances it can not be 
stated how much the results are affected by individual susceptibility 
or b}^ the operation of some as yet unknown factor or factors in the _ 
conveyance of or in the establishment of susceptibility (perhaps 
specific) to typhoid-fever infection. 
It may be readily understood how strains of the organism of a low 
degree of infectiveness (and of virulence) getting into milk, there 
undergoing tremendous multiplication and so being distributed in 
large doses, may cause outbreaks of typhoid fever. This view of low 
infectiveness and virulence of the organism being offset by large 
dosage is supported by some of the features observed in a number of 
the reported milk-borne outbreaks. For instance, short period of 
incubation, sudden onset and rapid decline of attack, reduced contact 
infectivity and low fatality rate. 
It is theoretically possible, however, that these features are due to 
large dosage alone. Thus, a large number of virulent organisms 
upon being introduced suddenly into relatively highly resistant 
tissues, a pronounced reaction occurs (sudden onset of definite symp- 
toms) with resulting formation of relatively large amount of anti- 
bodies (rapid decline of attack, reduced contact infectivity, etc.). 
The establishment of milk as the causative factor in an outbreak of 
typhoid fever is based on the following points : 
{a) A sudden and marked increase in the number of cases along 
the route of some dairyman, without a corresponding increase in the 
number of cases among persons li^fing in the same sections of the city 
but supplied with milk from other sources. In a town supplied largely 
or entirely by one dairyman a sudden increase in the number of cases 
would not implicate the milk unless other facts pointed to it and 
other factors could be excluded, but in large cities, where the people 
of practically every square are supplied with milk by two or more 
dairymen, an increase in the number of cases distinctly on the route 
of a given dairyman is quite easily determined. This fact alone is 
evidence that the milk is responsible, and if an investigation reveals 
that at a time corresponding to the period in which the group of cases 
along the dairyman’s route became infected there was at the dairy or 
45276°— Bull. 56—12 11 
