relation between the nervous and sanguiferous systems. 433 
unless they make their impression on a large part of this sys- 
tem. In the various experiments I have related, every part 
of the nervous system was stimulated individually, without 
the action of the heart being influenced, and the stimulus 
being the same, the force with which it acted on this organ, 
was always proportioned to the extent of surface to which 
it was applied. I could not find that it was of any importance 
what part of the brain was stimulated. Even stimulating the 
surface alone, either mechanically or chemically, immediately 
increased the action of the heart. The muscles of voluntary 
motion, on the contrary, we have seen, are wholly insensible 
to stimuli applied to the nervous system, except near the 
origin of the nerves. It is remarkable that while a rabbit 
perfectly retains its sensibility, and expresses great pain on any 
of the muscles being wounded, it exhibits no expression of 
pain whatever from the brain being sliced, until the knife ap- 
proaches the origin of the nerves or spinal marrow. 
Another circumstance, which appears to be of great impor- 
tance in tracing the cause of the different effects of stimuli ap- 
plied to the nervous system on the muscles of voluntary and in- 
voluntary motion, is, that the heart obeys a much less powerful 
stimulus than the muscles of voluntary motion do. We have 
seen that only the most powerful chemical stimulus affects 
them, while all that were tried readily influenced the action of 
the heart. Mechanical stimuli which, by bruising and dividing 
the parts, occasion the greatest possible irritation, are best 
fitted to excite the muscles of voluntary motion. Chemical 
stimuli, indeed, from their effects on the heart, we should 
consider the most powerful. But their greater effect on this 
organ is readily explained, by the influence of stimuli applied 
mdcccxv. 3 K 
