480 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1944 
county shall be accredited in which there is an average annual death 
rate of 10 or less per 100,000 and a tuberculosis infection rate, as evi- 
denced by a positive tuberculin test, of less than 15 percent among 
high-school seniors. At least 7 of Minnesota’s 97 counties have already 
qualified for this honor. 
Casual reference to tuberculous infection as something quite time 
extensive has probably been confusing to the reader. Reference to 
figure 1 should assist in the understanding of the early stages in the 
host-parasite relationship of the tubercle bacillus and man. 
Some diseases are short-lived and decisive. The patient is sick 2 or 3 
days and then is about his work. Such a disease is a mild attack of 
influenza. In typhoid fever, on the other hand, the patient may be ill 
6 weeks or more, and there is a further period of convalescence to add 
Infiltration resulting in a 
positive X-ray diagnosis 
Sensitization. 
Entrance of 
bacilli into 
bodye = = 
In the great majority of 
cases no clinical symptoms 
appear and indeed in man 
such it is impossible to 
Failure of find any visible X-ray 
bacilli to evidence of tuberculous t 
establish infection;i.e.,the 
themselves sensitizing lesion is 
in the obscures 
body. 
Figure 1.—The result of the invasion of the body by tubercle bacilli. 
to the 6 weeks’ loss of time from work. In tuberculosis there may be a 
very gradual onset involving 2 or 3 years before the patient has any 
symptoms at all. Probably every person in the United States has 
swallowed or inhaled at least one living tubercle bacillus even in this 
day of allegedly fine progress in the elimination of tuberculosis. In 
half, or more than half of us, the microbe did not successfully invade 
the body. (Some of the points involved in the host-parasite relation- 
ship bearing on this point are fascinating to contemplate but difficult 
to set in order, and they are graphically suggested in figure 2.) 
Shortly (2 to 7 weeks) after the tubercle bacillus has invaded the 
body the tissues become sensitized and the host is altered profoundly, 
just how profoundly we do not yet know. The elicitation of a posi- 
tive tuberculin test from such a person is only one aspect of the mat- 
