Page:Popular Science Monthly Volume 12.djvu/441

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THE HYGIENIC INFLUENCE OF PLANTS.

is something the same with the pleasures of life as with the pleasures of the table; we must relish our food if it is to do us good. What good will the most nourishing diet do me if it creates disgust? Prof. C. Voit has clearly pointed out, in his experimental researches into diet, the great value of palatable food, as well as nourishment, and how indispensable a certain variety in our meals is. We think we are only tickling the palate, and that it is nothing to the stomach and intestines whether food is agreeable to the palate or not, since they will digest it, if it is digestible at all. But it is not so indifferent, after all; for the nerves of the tongue are connected with other nerves and with the nerve-centres, so that the pleasures of the palate, or some pleasure, at any rate, even if it is only imagination, which can only originate in the central organ, the brain, often has an active effect on other organs. This is a matter of daily experience. If you put your finger down your throat, you produce retching; many people have only to think of anything disgusting to produce the effect of an emetic, just as the thought of something nice makes the mouth water just as much as tasting the most dainty morsel. Voit showed me one of his dogs with a fistula in the stomach. So long as this dog is not thinking of food, his stomach secretes no gastric juice, but no sooner does he catch sight of a bit of meat, even at a distance, than the stomach prepares for digestion and secretes gastric juice in abundance. Without this secretion the assimilation of nourishment would be impossible. If, therefore, some provocatives induce and increase certain sensations and useful processes, they are of essential value to health, and it is no bad economy to spend something on them.

I consider flowers in a room, for all to whom they give pleasure, to be one of the enjoyments of life, like condiments in food. It is certainly one of the most harmless and refined. We cannot live on pleasure alone; but, to those who have something to put up with in life, their beloved flowers perform good service.

The same may be said of private gardens and public grounds, and of the artistic perfecting of them. The more tastefully laid out, the better the effect. Though tastes differ, there is a general standard of taste which lasts for several generations, though it varies from time to time, and is subject to fashion. As their object is to give pleasure, public grounds should accord with the taste of the age, or aim at cultivating it. This is a justification for going to some expense for aesthetic ends.

The influence of vegetation on the soil is much more easy to determine than on the mind of man. Space fails me to go into all the aspects of this subject, and I will confine myself to some of the most obvious. The difference is most apparent on comparing the soil of a tract of land covered with wood with the soil outside, in other respects alike. The Bavarian Forest Department deserves great credit for having established meteorological stations with special reference to