"This test is very simple, Doctor Putnam," continued Craig, as I
placed the cage on the table and Kennedy unwrapped the sterilised
test-tubes. "A rabbit is inoculated with human blood, and after a
time the serum that is taken from the rabbit supplies the
material for the test.
"I will insert this needle in one of these rabbits which has been
so inoculated and will draw off some of the serum, which I place
in this test-tube to the right. The other rabbit has not been
inoculated. I draw off some of its serum and place that tube here
on the left--we will call that our 'control tube.' It will check
the results of our tests.
"Wrapped up in this paper I have the scrapings of the spot which
I found on the floor--just a few grains of dark, dried powder. To
show how sensitive the test is, I will take only one of the
smallest of these minute scrapings. I dissolve it in this third
tube with distilled water. I will even divide it in half, and
place the other half in this fourth tube.
"Next I add some of the serum of the uninoculated rabbit to the
half in this tube. You observe, nothing happens. I add a little
of the serum of the inoculated rabbit to the other half in this
other tube. Observe how delicate the test is--"
Kennedy was leaning forward, almost oblivious of the rest of us
in the room, talking almost as if to himself.
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