This chapter would not be complete without an intimation of the rôle of buffers in the sea water and the blood, by which the reaction of these media is prevented from changing in a way injurious to the organism. These buffers are the carbonates and phosphates. Instead of saying that the organisms are adapted to the medium, L. Henderson has pointed out the fitness of the environment for the development of organisms and one of these elements of fitness are the buffers against alterations of the hydrogen ion concentration.[274] The ratio in which the salts of the different metals exist in the sea water is another. It is obvious that the quantitative laws prevailing in the effect of environment upon organisms leave no more room for the interference of a “directing force” of the vitalist than do the laws of the motion of the solar system. [274] Henderson, L., _The Fitness of the Environment_. See also Michaelis, L., _Die Wasserstoffionenconzentration_. Berlin. 1914. CHAPTER XII ADAPTATION TO ENVIRONMENT 1. It is assumed by certain biologists that the environment influences the organism in such a way as to increase its adaptation. Were this correct it would not contradict a purely physicochemical conception of life; it would only call for an explanation of the mechanism by which the adaptation is brought about. There are striking cases on record which warn us against the universal correctness of the view that the environment causes an adaptive modification of the organism. Thus the writer pointed out in 1889 that positive heliotropism occurs in organisms which have no opportunity to make use of it,[275] _e. g._, _Cuma rathkii_, a crustacean living in the mud, and the caterpillars of the willow borer living under the bark of the trees. We understand today why this should be so, since heliotropism depends upon the presence of photosensitive substances, and it can readily be seen that the question of use or disuse has nothing to do with the production of certain harmless chemical compounds in the body. A much more striking example is offered in the case of galvanotropism. Many organisms show the phenomenon of galvanotropism, yet, as the writer pointed out years ago, galvanotropism is purely a laboratory product and no animal has ever had a chance or will ever have a chance to be exposed to a constant current except in the laboratory of a scientist. This fact is as much of a puzzle to the selectionist and to the Lamarckian (who would be at a loss to explain how outside conditions could have developed this tropism) as to the vitalist who would have to admit that the genes and supergenes indulge occasionally in queer freaks and lapses. The only consistent attitude is that of the physicist who assumes that the reactions and structures of animals are consequences of the chemical and physical forces, which no more serve a purpose than those forces responsible for the solar systems. From this viewpoint it