THE HYGIENIC INFLUENCE OF PLANTS. 417 



some becoming old and indisposed to erupt unless angered by throw- 

 ins: stones down the throat. 



It is evident, however, that Bunsen's theory of geyser-eruption is 

 independent of his theory of geyser-formation. A tube or fissure of 

 any kind, and formed in any way, if long enough, would give rise to 

 the same phenomena. The Yellowstone geysers have mounds or chim- 

 ney-like cones, but it is by no means certain that the whole length of 

 their eruptive tubes has been built up by siliceous deposit. Bunsen's 

 theory of eruption none the less, however, applies to these also. The 

 more chimney-like form of the craters in the case of the Yellowstone 

 geysers is probably due to the greater abundance of silica in solution. 



THE HYGIENIC INFLUENCE OF PLANTS. 



Br MAX VON PETTENKOFER. 



THE animal kingdom is, as we know, dependent on the vegetable 

 kingdom, which must have existed on the earth before men and 

 animals could live upon it. We may, therefore, rightly call plants 

 children of the earth. But, in so doing we use the language of meta- 

 phor, as when we speak of " Mother Earth." The earth does not di- 

 rectly bring forth either plants or animals. Every plant is the child 

 of a mother-plant, descends from one of its own kind like ourselves; 

 but plants derive their nourishment directly from earth, air, and 

 water, and, although generated by plants, are nourished directly by 

 the inorganic breasts of Nature, and imply no other organic life but 

 their own. Had plants a voice, they would more correctly speak of 

 "Mother Earth" than ourselves. 



Plants live directly on the lifeless products of earth, and we live 

 directly on the products of plants or on animals which live on them ; 

 our existence implies other organic life, and our nourishment is not 

 derived so directly from the earth as that of plants. Since the vege- 

 table world comes between us, ice should rather call earth our grand- 

 mother than our mother. At all events it is an affectionate rela- 

 tionship. 



We have a natural feeling of close affinity with the vegetable 

 world, which expresses itself not only in our love of foliage and flow- 

 ers, but in our fondness for metaphors derived from the vegetable 

 world and its processes. If we were to reckon up how many meta- 

 phors in every-day life and in poetry are derived from the vegetable 

 world, and how many from other spheres of Nature, we should find a 

 great excess of the former. 



Our material relations to plants are also very numerous. The 



question we are now concerned with is not what food or what medi- 

 vol. xii. 27 



