IS LEPROSY A TELLURIC DISEASE ? 
781 
leper. You will see this at once, too, because Australian experience 
of leprosy in whites shows, beyond possibility of doubt, that this 
disease can be contracted quite independently of intimate contact 
with lepers. Our own experience shows us that this can happen, and 
even that it most usually is the case. Now, if known long-continued 
contact with lepers is most often supported without the disease being 
communicated — I mean, of course, without any second case occurring 
in the household of which the solitary primary leper was a member, 
and therefore without even apparent or prima facie evidence of com- 
municability being afforded — we are logically warranted thereby in 
saying, not in general terms, that leprosy is a disease difficult to 
contract, or one to which a majority of persons are naturally resistant 
(for that would beg the question), but, at most, that at all events lepra 
is a disease very difficult to contract from lepers. And therefore, 
when on the other hand we observe that lepra very often does occur 
in persons who have been in no conscious contact with any leper, 
when we notice that close or long-continued contact with lepers is 
certainly not essential, we get (as it seems to me) a very important 
suggestion. The two facts taken together — for they are both well- 
established, commonly known, and such, moreover, as might be safely 
relied upon even if there were no other evidence of them than our 
own Australian experience — these two facts taken together seem to 
me to point to this : That leprosy may be a disease not at all difficult 
to contract, provided the virus in efficient form be met with under 
favourable external circumstances, among which presence of an actual 
leper is probably not essential. 
There are two views which must be mentioned after setting out the 
foregoing argument. They are entertained by writers who either do 
not explicitly state that prolonged and intimate contact with lepers is 
necessary, or who implicitly deny its necessity by relying on indirect 
communication of the virus by the sick. 
Those who do not explicitly require long-continued contact have 
pointed out that, as a very long latent period is commonly conceded to 
leprosy, it must always be difficult, and sometimes impossible, to trace 
the human source of’ the infection. I think this remark must have 
originated with someone not in the habit of tracing the course of 
outbreaks of communicable disease. If individual cases of lepra were 
alone to be examined, it would have great force. But it would have 
equal force if examination of individual occurrences of influenza or 
cholera were examined to learn whether those diseases were communi- 
cable by the sick, brief as the latent period is in them. It is not 
thus, in short, that the communicability of diseases is, or can be, 
established. The communicability of diseases can be examined only 
by comparison of the broadest epidemiological facts. 
The other point has been indirectly raised bv those who have 
suggested that lepra was maintained, not by direct communication 
with the sick, but by indirect communication — that is to sav, by way 
of the soil infected by bacteridia cast off from the bodies of (tuberous) 
lepers. This view' seems to have been based on an analogy with 
tuberculosis. In that disease living bacilli are known to be cast off, 
and are known to be capable of surviving in efficient form for long 
after they have left the body. 
