21 
1 again emphasizing the importance of the host's role in 
2 successful pathogenesis by microorganisms. 
3 Insofar as mechanisms of pathogenesis are 
4 concerned, much again is known about the established 
5 pathogens of man. Group A streptococci make M protein 
g which conveys an antiphagocytic resistence to the bearer. 
7 Pneumococci make a capsular polysacchar ide which serves 
8 a similar function. Diphtheria bacilli are entirely 
9 innocuous unless they themselves are infested with a 
10 lysogenic phage, and even then, proper iron concentrations 
H and other environmental conditions are necessary before 
12 toxin production can proceed, and so forth. 
13 It is interesting to note that even in the case 
14 of drug resistence, where much of our new infectious disease 
15 problems lie, the multiply drug-resistant tubercle bacillus 
16 has reduced virulence as a correlative property. 
17 I have conducted this brief exercise in medical 
18 microbiology to establish several points: First, that 
19 emphasis on the human host working in the environment of 
20 potentially new microorganisms is appropriate; second, that 
21 dosage is an important element in known pathogenetic micro- 
22 bial disease, and so sensible efforts at containment, with 
23 particular attention paid when microorganisms are at high 
24 concentrations, can be imposed with a degree of confidence; 
25 thirdly, that known, highly virulent pathogens are in 
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