The influence transmitted to these glands causes,
as there is good reason to believe, the relaxation of the muscular
coats of the smaller arteries; this allows more blood to permeate
the glandular tissue, and this induces a free secretion of tears.
When the small arteries of the face, including those of the retina,
are relaxed under very different circumstances, namely, during an
intense blush, the lacrymal glands are sometimes affected in a like manner,
for the eyes become suffused with tears.
It is difficult to conjecture how many reflex actions have originated,
but, in relation to the present case of the affection of the lacrymal
glands through irritation of the surface of the eye, it may be worth
remarking that, as soon as some primordial form became semi-terrestrial
in its habits, and was liable to get particles of dust into its eyes,
if these were not washed out they would cause much irritation;
and on the principle of the radiation of nerve-force to adjoining
nerve-cells, the lacrymal glands would be stimulated to secretion.
As this would often recur, and as nerve-force readily passes along
accustomed channels, a slight irritation would ultimately suffice
to cause a free secretion of tears.
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