492 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1944 
TABLE 3.—Tracing medical students, originally tuberculin negative 
Total 
Of these, 
patel Number | Number | number 
- | of these | who com-} graduat- 
Class tubereulin| who left | pleted all] ing tu- | Percent 
rs cake school 4years | berculin 
men negative 
Graduating November 1943____.....-___--...-.--____- 35 5 30 22 73 
Graduating. February 1943... .00-22-!_-.- 2-2-2 42 6 36 21 58 
Gradtintine 1042) 2 oer eRe 5 ee Le eae ed 40 3 37 23 62 
Gredchin ge POAT ai ees ee) ieee ae Oe 21 5 16 tf 44 
GYradaating 1940 Oe fe he ee Oe ae VO 24 6 18 13 72 
Grdgunbine OSA Fes he Re pes a ee 30 6 24 ll 46 
Totaly sehe Whee ah Nk Boe es Se ae 192 31 161 97 60 
Of the 64 students, originally tuberculin negative, who became tuberculin positive, 4 developed clinical 
tuberculosis—1 man losing 2 years, 1 losing 1 year, and 2 no time loss. All 4 at present are in fine physical 
condition. 
We were further impressed by the fact that a considerable number of 
medical students who gave weakly positive tuberculin tests later be- 
came negative. Students were not followed prior to 1939 through all 
semesters; hence the figures on this point do not include all our ap- 
proximately 1,000 students. Of those followed (666), however, 134 
have reacted only to the strong dose of purified protein derivative. 
This represents a low grade of sensitivity due perhaps to an almost 
negligible original sensitizing lesion or to a lesion almost completely 
sterilized or possibly, in an occasional case, to a nonspecific reaction. 
Nine classes are included in this aspect of the study, four of which are 
still in school, on whom obviously the data are not yet complete. In 
the five classes concerned that have graduated 56 showed weakly 
positive reactions as freshmen. Of these, 18 showed stronger reac- 
tions as they progressed through school, indicating some sort of sensi- 
tizing or immunizing process at work. Six became entirely negative 
and one became weaker in tuberculin reactivity, 22 remained the same, 
and a few of the original freshmen did not graduate. Among the 666 
students of these nine classes 319 were positive to some strength of 
tuberculin as freshmen (47.9 percent). Of these, 134 (42.0 percent) 
were weak reactors. Among the 323 students of the last four classes 
there were 139 reacting to tuberculin (48.0 percent), of whom 78 were 
only weakly positive (56.1 percent). Among the 348 students in this 
series who have graduated there were 180 tuberculin reactors (52.4 
percent), but of these only 56 were weak reactors (31.1 percent). 
Several points may be made regarding these data. An environ- 
ment containing tubercle bacilli does not prevent a certain number 
of weakly positive tuberculin reactors from becoming negative. These 
individuals may be thought of as resistant strains of the human race. 
Our newer students are showing not only a lower total tuberculariza- 
tion rate but also a tubercularization of less intensity. Tubercle ba- 
cilli in the environment are doing less to medical students than 
