VI. The movements of their adapted fluids in the various vessels of the body are carried forwards by the actions of those vessels in consequence of two kinds of stimulus, one of which may be compared to a pleasurable sensation or desire inducing the vessel to seize, and, as it were, to swallow the particles thus selected from the blood; as is done by the mouths of the various glands, veins, and other absorbents, which may be called glandular appetency. The other kind of stimulus may be compared to disagreeable sensation, or aversion, as when the heart has received the blood, and is stimulated by it to push it forwards into the arteries; the same again stimulates the arteries to contract, and carry forwards the blood to their extremities, the glands and capillaries. Thus the mesenteric veins absorb the blood from the intestines by glandular appetency, and carry it forward to the vena portarum; which acting as an artery contracts itself by disagreeable stimulus, and pushes it to its ramified extremities, the various glands, which constitute the liver.
It seems probable, that at the beginning of the formation of these vessels in the embryon, an agreeable sensation was in reality felt by the glands during secretion, as is now felt in the act of swallowing palatable food; and that a disagreeable sensation was originally felt by the heart from the distention occasioned by the blood, or by its chemical stimulus; but that by habit these are all become irritative motions; that is, such motions as do not affect the whole system, except when the vessels are diseased by inflammation.
OF THE SECRETIONS OF SALIVA, AND OF TEARS, AND OF THE LACRYMAL SACK.
I. _Secretion of saliva increased by mercury in the blood._ 1. _By the food in the mouth. Dryness of the mouth not from a deficiency of saliva._ 2. _By Sensitive ideas._ 3. _By volition._ 4. _By distasteful substances. It is secreted in a dilute and saline state. It then becomes more viscid._ 5. _By ideas of distasteful substances._ 6. _By nausea._ 7. _By aversion._ 8. _By catenation with stimulating substances in the ear._ II. 1. _Secretion of tears less in sleep. From stimulation of their excretory duct._ 2. _Lacrymal sack is a gland._ 3. _Its uses._ 4. _Tears are secreted, when the nasal duct is stimulated._ 5. _Or when it is excited by sensation._ 6. _Or by volition._ 7. _The lacrymal sack can regurgitate its contents into the eye._ 8. _More tears are secreted by association with the irritation of the nasal duct of the lacrymal sack, than the puncta lacrymalia can imbibe. Of the gout in the liver and stomach._