PHILOSOPHICAL 
TRANSACTIONS. 
I. The Croonian Lecture. On the Functions of the Heart and 
Arteries. By Thomas Young, M. D. For. Sec. R. S. 
Read November 10, 1808. 
The mechanical motions, which take place in an animal body, 
are regulated by the same general laws as the motions of in- 
animate bodies. Thus the force of gravitation acts precisely 
in the same manner, and in the same degree, on living as on 
dead matter ; the laws of optics are most accurately observed 
by all the refractive substances belonging to the eye ; and 
there is no case in which it can be proved, that animated bodies 
are exempted from any of the affections to which inanimate 
bodies are liable, except when the powers of life are capable 
of instituting a process, calculated to overcome those affections, 
by others, which are commensurate to them, and which are 
of a contrary tendency. For example, animal bodies are in- 
capable of being frozen by a considerable degree of cold, 
because animals have the power of generating heat ; but the 
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