Future of Infectious and Malignant Diseases 
seems to have become identified with the episome, an extra- 
chromosomal genetic unit which may multiply independently 
of the chromosome or as an addition to it. This makes the factor 
almost invulnerable, since it can be either transmitted by 
conjugation or transduction or become attached to the chromo- 
somes and associated with the genetic mechanism. 
Another major danger in attempting to eradicate disease lies 
in the possible consequences of an upset in the ecological 
balance between man and his micro-organisms. The partial or 
total elimination of any microbial species can lead to the 
appearance of new, often hitherto unrecognized infectious 
agents which would tend, in the human body, to take the place 
of the bugs which had been driven out. Even now there is an 
increasing number of mycobacterial infections which are not 
true tuberculosis, and many cases of bacterial meningitis are 
caused by microbes which have not previously been known to 
play a role in the aetiology of the disease. 
Eradication of malaria is a slogan for the immediate future; 
yet it has already been demonstrated that monkey malaria can 
be transmitted to man, and attempts at eradication of one 
parasite will only make possible its replacement by another 
which may be much harder to deal with. In general, the list of 
non-pathogenic organisms which may take the place of the 
“eradicated”? pathogens in the human body is probably in- 
exhaustible. Many of them have never been observed in 
connexion with a disease, and yet they may become a greater 
cause of alarm than the pathogenic organisms of our immediate 
acquaintance. 
Eradication of poliomyelitis is another aim of the future 
public health man. What for? Even if we could not control 
outbreaks of polio as we do today, it should be remembered 
that polio is essentially a mild infection of the gastrointestinal 
tract which runs, in the vast majority of cases, an asymptomatic 
course. ‘The virus is almost a normal inhabitant of human 
intestines, and its “‘eradication”’, which I hope will never take 
place, could lead to its replacement by other unrelated viral 
agents which might treat the human host much less mercifully 
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