No, we freely admit that
the systems of levers in the human machine are quite unlike those of a
motor cycle. They are more simple, and it is easy to find in our bodies
examples of all the three orders of levers. The joints at which bony
levers meet and move on each other are very different from those we find
in motor cycles. Indeed, I must confess they are not nearly so simple.
And, lastly, I must not forget to mention another difference. These
levers we are going to study are living--at least, are so densely
inhabited by myriads of minute bone builders that we must speak of them
as living. I want to lay emphasis on that fact because I did not insist
enough on the living nature of muscular engines.
[Illustration: Fig. 1.--Showing a chisel 10 inches long used as a lever
of the first order.]
We are all well acquainted with levers. We apply them every day. A box
arrives with its lid nailed down; we take a chisel, use it as a lever,
pry the lid open, and see no marvel in what we have done (Fig. 1). And
yet we thereby did with ease what would have been impossible for us even
if we had put out the whole of our unaided strength.
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