The experiment repeated with another frog gave the same
result. Why? It can hardly be because the frog is cold-blooded,
for many birds also seem, to be immune, and their blood is warmer
than man's.
Next, I took a live frog and rubbed it on my hand over an area
marked out with lead pencil; at first the place was wet, but in a
few seconds dry and rather shiny. I held up my hand till 50 mosquitoes
had alighted on it and begun to bore; of these, 4 alighted on the
froggy place, 3 at once tumbled off in haste, but one, No. 32, did
sting me there. I put my tongue to the frog's back; it was slightly
bitter.
I took a black-gilled fungus from a manure pile to-day, rubbed a
small area, and held my hand bare till 50 mosquitoes had settled
and begun to sting; 7 of these alighted on the fungus juice, but
moved off at once, except the last; it stung, but at that time the
juice was dry.
Many other creatures, including some birds, enjoy immunity, but
I note that mosquitoes did attack a dead crane; also they swarmed
onto a widgeon plucked while yet warm, and bored in deep; but I
did not see any filling with blood.
There is another kind of immunity that is equally important and
obscure. In the summer of 1904, Dr. Clinton L. Bagg, of New York,
went to Newfoundland for a fishing trip. The Codroy country was,
as usual, plagued with mosquitoes, but as soon as the party crossed
into the Garnish River Valley, a land of woods and swamps like the
other, the mosquitoes had disappeared. Dr. Bagg spent the month of
August there, and found no use for nets, dopes, or other means of
fighting winged pests; there were none. What the secret was no one
at present knows, but it would be a priceless thing to find.
Now, lest I should do injustice to the Northland that will some
day be an empire peopled with white men, let me say that there are
three belts of mosquito country the Barren Grounds, where they are
worst and endure for 2 1/2 months; the spruce forest, where they
are bad and continue for 2 months, and the great arable region of
wheat, that takes in Athabaska and Saskatchewan, where the flies
are a nuisance for 6 or 7 weeks, but no more so than they were in
Ontario, Michigan, Manitoba, and formerly England; and where the
cultivation of the land will soon reduce them to insignificance,
as it has invariably done in other similar regions. It is quite
remarkable in the north-west that such plagues are most numerous
in the more remote regions, and they disappear in proportion as
the country is opened up and settled.
