526 



SCIENCE 



[N. S. Vol. LI. No. 1326 



of the protoplasmic system, i. e., upon 

 metabolism. 



2. This metabolism involves a continual 

 construction of complex specific compounds — 

 typically compounds of high chemical poten- 

 tial — to replace those disintegrated (as a re- 

 sult or oxidation or otherwise) in the energy- 

 yielding or otherwise destructive processes of 

 protoplasm. 



3. The rate and in part the character of 

 both the energy-yielding and the constructive 

 metabolism are readily influenced by changes 

 in the external conditions: i. e., protoplasm 

 is a characteristically irritable system — one of 

 unstable equilibrium. 



4. The ratio of constructive to destructive 

 metabolism may vary widely under different 

 conditions; excess of construction over de- 

 struction involves growth; equality of the two 

 is equilibrium, implying a stationary condi- 

 tion as regards size and properties; while 

 excess of destruction leads to regression, as 

 in starvation. Obviously regression, if suflS.- 

 cient, must impair fimctional capacity and 

 eventually lead to death. 



5. The power of growth is thus inherent or 

 potential in all forms of protoplasm during 

 life. Those pathological problems which re- 

 late to excessive or otherwise abnormal growth 

 or proliferation (e. g., the case of tumors) 

 thus require for their scientific solution a 

 knowledge of the physico-chemical conditions 

 of normal growth. 



It is evident, since growth is an inherent 

 property of the living system — i. e., since the 

 continuance of the living state depends on 

 this power of specific construction — that the 

 problems just cited relate themselves directly 

 to the general group of problems having refer- 

 ence to the essential physico-chemical consti- 

 tution of protoplasm. The protoplasmic sys- 

 tem is primarily a growing or synthesizing 

 system, at the same time as it is a system 

 which continually yields material and energy 

 to the surroundings through the chemical 

 breakdown of certain components. The chief 

 aim of general physiology is to understand 

 the type of physical and chemical constitution 



that makes possible chemical activities of this 

 general kind. 



Experiment shows that destroying the 

 structure of protoplasm, by mechanical or 

 other means, destroys most (though not aU) 

 of its chemical activity (including the latter's 

 susceptibility to electrical influence), and in 

 particular its power of specific synthesis or 

 growth. Hence this power must depend on 

 the special structure of the system. The 

 chemical reactions constituting metabolism 

 take place within a field or substrattmi having 

 a special type of structure (i. e., arrangement 

 of phases) ; and the nature and rate of the 

 metabolic reactions are controlled by the struc- 

 tural conditions present. These structural 

 conditions are themselves produced by the 

 growth of the system itself, or of another 

 system having similar properties. 



It must be recognized that the problem of 

 the fundamental constitution of living proto- 

 plasm underlies all of the problems of biology 

 — including ultimately those of medicine, as 

 a branch of applied biology. It is therefore 

 all-important from the practical as well as 

 from the purely scientific standpoint that 

 this problem should be the subject of continual 

 and active study and investigation. 



Physical Processes of Fundamental Im- 

 portance in Protoplasmic Activities. — The re- 

 search of the past fifteen years has made 

 especially clear the importance of surface- 

 processes in the activity of living matter. 

 The behavior and properties of colloids (the 

 substances composing most of the solid mate- 

 rial of protoplasm) are largely determined by 

 surface conditions (adsorption, variations of 

 phase-iboundary potentials, interfacial ten- 

 sions). Electrical stimulation depends upon 

 sudden changes in the electrical polarization 

 of the semi-permeable surfaces of the irritable 

 cell. Protoplasmic movement (muscular con- 

 traction, etc.) is almost certainly due in most 

 cases to the changing surface-tension of the 

 structural elements composing the contractile 

 fibrils. Growth processes show various sig- 

 nificant resemblances to structure-forming 

 processes occurring under the influence of local 

 electrolysis at metallic siirfaces in contact 



