No. 5S2] SIGNIFICANCE OF INTERNAL CONDITIONS 325 



other than vitalism. The organisms may be, under cer- 

 tain conditions at least, more variable than the environ- 

 ment. These considerations apply also to those simple 

 organisms which are the cellular constituents of a larger 

 body. Certain of the higher vertebrates, in which, as 

 has been indicated, the influence of the environment is 

 probably less than in some of the lower forms, are more 

 variable than certain of the lower vertebrates. 



It is a fair inference from the facts cited in the various 

 papers referred to, that certain characteristics of living 

 matter, such as its slight degree of alkalinity, and its rel- 

 atively great specific heat, may be regarded as the direct 

 automatic and inevitable results of the properties of the 

 environment. Other characteristics, as the peculiar type 

 of the nervous system, are not so obviously the direct and 

 inevitable result of the environment, and these may be 

 regarded, for some time to come, as adaptations to the 

 environment or to the general conditions of existence in 

 which the particular organism is able to live and perpetu- 

 ate itself. 



A statement of the general problem may now be made. 

 Two general classes of organisms live in a relatively con- 

 stant environment, so far as the general internal condi- 

 tions of the organism are concerned. (1) For example, 

 the lower marine organisms of fairly limited distribution 

 live in an external environment which changes but little 

 in temperature, osmotic pressure, inorganic salt content, 

 neutrality or faint alkalinity, oxygen and carbon dioxide 

 concentration, and soluble nitrogen compounds. Tem- 

 perature and amounts of light may vary somewhat 

 throughout the year, but the temperature changes in the 

 given region of the ocean are less in magnitude than the 

 temperature changes over a corresponding area of land. 

 The osmotic and inorganic salt relationships of organism 

 and environment alike vary but little. Nor does the or- 

 ganism, in general, maintain within itself, any purely 

 physico-chemical condition differing greatly from that in 

 the general external environment. This does not pre- 



