PETERS. — METABOLISM AND DIVISION IN PROTOZOA. 501 



recognize in the permeability of the cell-membrane or the protoplasmic 

 alveoli a fundamentally important, but thus far often undetermined, 

 factor. Without the determination of this factor physico-chemical ex- 

 planation cannot proceed far. 



These considerations lead to the following conception of the functions 

 of the salts normally occurring in cells. The activity of the organism, 

 in so far as it is dependent upon the physiological salts, depends, first of 

 all, upon the qualitative nature of the constituent salts, that is, the func- 

 tion of these salts is primarily constitutive. In the activity of the organ- 

 ism they do service by virtue of their native qualities. If the organism 

 had a different normal composition it would no longer exhibit the same 

 reaction (physiological, chemical, physical) by which it now preserves its 

 identity and individuality. 



Secondly, the reactions of the organism depend, so far as they depend 

 at all upon the physiological salts, upon the relative proportions of these 

 to one another. Their function is quantitative as well as constitutive. 

 A change in these proportions outside the normal limits of variation, 

 would result, if successful, in loss of identity, if unsuccessful, in disease 

 or death. 



This theory by no means asserts that the salt which we know as a com- 

 pound must exist as such in the organism. But the modified qualities, or 

 energies of the substances contribute to and determine the activities of the 

 organism, by virtue of their constitutive and quantitative relations to it. 



From one point of view, at least, the organism is an organization of 

 various substances, and the word organization means neither more nor 

 less than correlation. If we choose to take the most advanced physico- 

 chemical point of view, we may describe an organism as a specific cor- 

 relation of energies. 



The principles of constitutive and quantitative functions are nearly 

 axiomatic. With less certainty, but yet with a large degree of probabil- 

 ity, we can make a third proposition, which is derived from a considera- 

 tion of the facts of adjustment. What indication do these give of the 

 internal constitution of the cell ? The external medium to which the cell 

 is normally adjusted represents more or less closely the internal qualitative 

 and quantitative constitution of the cell This statement does not neces- 

 sarily apply to the external medium of the whole plant or animal body, 

 but it does apply to the liquid media in which the majority of cells 

 pass their entire existence. Further, the proposition is not intended to 

 exclude the possible presence in the medium of substances to which the 

 cell is approximately indifferent. 



