[Footnote 8: The true order of the occurrence of these changes is:--On the second day the urine becomes high-coloured; in a day or two later the skin assumes a yellow tint; and, in very severe cases, within the first week or two, the sweat, the milk, the tears, the sputa, and the serum in the thoracic and abdominal cavities, become of a more or less decided yellow hue.]
It is now a well-established fact that all secretions are under the direct influence of the nervous system. Stimulate a nerve supplying a gland, and secretion is accelerated; stop the nervous action, and secretion is as instantaneously arrested. Again, just in the same way as volition can produce or suspend muscular movement, mental influence can hasten or retard glandular secretion. As an illustration of this fact, I need only call to mind the influence the mere sight of food has in exciting the salivary secretion, and the effect of bad news in arresting it. Exactly the same influence as is here alluded to, is exerted by the mind over the biliary function. If, for example, { 23} as Bernard first observed, a dog with a biliary fistula be caressed, the secretion of bile is actively continued; if, on the other hand, the animal be suddenly ill-used, the secretion of bile is instantly arrested. If he be again caressed, the secretion is re-established, and the bile flows drop by drop from the end of the cannula. Here the influence is entirely produced through the intervention of the nervous system; and if such effects as are above described occur in the dog, we can surely have little difficulty in understanding how the biliary secretion can be influenced in the highly-developed organization of the human being. Indeed, every one must have felt how quickly sad tidings received during a meal not only destroy the appetite and retard digestion, but occasionally alter the complexion. This effect, that all of us must have experienced in a slight degree in our own persons, several may have observed to a greater extent in the persons of others, even to the production of well-marked jaundice. At this very time I have under my care a young married lady, who during the last two years has twice suffered from an attack of jaundice induced by witnessing her child in convulsions, and this I regard as an example of jaundice from enervation.