The nerves of the gastric glands can be stimulated by various agencies which influence the central nervous system, and thus provoke appetite; for instance, sight, for we know of old how the sight of tasty dishes provokes our appetite. Professor Pawlow, of St. Petersburg, has shown by experiments on dogs, in whose stomachs he had made a fistula, that merely showing them a piece of meat was sufficient to cause them to secrete a large quantity of stomach juice. Umber has also shown on man that optic influence was able to produce the secretion of gastric juice. In addition to sight, smell produces similar results. Professor Bickel,[305] of Berlin, has experimented on a girl of 23, who, after an injury from caustic potash, had to have a fistulous opening made into her stomach, her œsophagus being completely strictured. By holding steaming hot soup under her nose he caused the secretion of a clear stomach juice to run through the open fistula. Footnote 305: Congress für Innere Medicin, 1904. The secretion of the stomach juice can also be produced by the sense of taste. Professor Bickel showed this in the above case by placing on the girl’s tongue a solution of sugar, and again of salt, and there followed each time a secretion of stomach juice. Pawlow has also proved this by ingenious experiments on dogs. After making a fistula in their œsophagus he gave them pieces of meat to eat, which, on being swallowed, fell out again by the open œsophagus, so that they never reached the stomach; and yet the taste of the meat and chewing were sufficient to cause the production of a large amount of gastric juice. Thus the secretion of the gastric juice is under nervous influence. But if pleasant nervous impulses are able to promote its secretion, on the other hand, as shown by the observations of Beaumont, and also of Sommerfeld on men, disagreeable impressions are able to check it. Bickel and Sasaki have also observed this to have occurred in persons who have been in a state of anger, which coincides with our own observations that when we are in a depressed mental condition, or when we receive disagreeable news, we often lose our appetite. If, therefore, we want to eat with relish we must put aside all mental pre-occupation and worry, and go to the table in a cheerful mood. Persons of a melancholy temperament seldom have an appetite, and in melancholia there is often a refusal to eat, so that nourishment has to be maintained artificially. When any one has been working in the open air all day and is of a cheerful disposition, he will not need anything appetizing to make him eat. By his work he has digested his food easily, his body craves for more to keep up his energy, and his empty stomach requires to be filled; he will be hungry and have a good appetite without any artificial stimulus.