THE HYGIENIC INFLUENCE OF PLANTS. 425 



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 indiflerent, 

 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 peo- 

 ple 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 abun- 

 dance. 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 cer- 

 tainly one of the most harmless and refined. We cannot live on pleas- 

 ure 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 cul- 

 tivating 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 deter- 

 mine 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 



