106 
PHYSIOLOGICAL ACTION OF ATROPINE. 
third nerve. Perhaps in those cases where the narcotic is 
observed to increase the size of the already dilated pupil, 
some small twigs of the nerve remain incompletely paralysed. 
As no effect was observed to follow the application of atropine 
in the experiment just cited, I divided the cervical sympa- 
thetic on the same side of the neck. The iris gradually 
contracted, but not to the same marked extent as in the 
cases where the sympathetic was alone divided ; in fact, the 
pupil remained permanently in a state of half dilatation and 
half contraction. The circular as well as the radiating fibres 
of the iris being paralysed by the section of their respective 
nerves, the contractile property of the muscular fibrillae was 
brought into abeyance, and there could be neither on the 
one nor the other side an excess of action so as to produce 
either a condition of dilatation or contraction of the pupils. 
This, indeed, is an exactly similar condition to that which 
supervenes when, after section of the sympathetic, a solution 
of atropine is dropt into the eye. We have seen, both in the 
experiments performed by Professor Sharpey and by myself, 
that atropine can not cause dilatation of the pupil by stimu- 
lating the cervical sympathetic ; and, I think we are justified 
in the present state of our knowledge, in continuing to 
attribute the influence of atropine upon the pupil, to its 
possessing the power of paralysing the third pair of nerves. 
In a similar manner 1 would account for the effect of opium 
and other substances possessing the power of inducing con- 
traction of the pupil, not to their stimulating the third pair, 
but to their paralysing the sympathetic which governs the 
dilatation of the pupil. 
In conclusion, the foregoing experiments, I think, tend to 
prove : — 
1. That atropine does not possess the power of dilating 
the pupil by directly stimulating the sympathetic nerve. 
2. That to act upon the pupil it must, as Mr. B. Bell 
says, first be absorbed. 
3. That it can act, not only on the periphery, but also on 
the roots of the nerves. 
4. The probable action of atropine or belladonna in dilating 
the pupil, depends on its paralysing the ciliary branches of 
the third pair of nerves, ancl not on its stimulating the 
filaments of the sympathetic, which supply the radiating 
fibres of the iris. — Edinburgh Medical Journal . 
