INTRODUCTION 



William Seifriz 

 The contributors to this symposium on protoplasm will deal with 

 present-day concepts on the structure of living matter. A brief 

 recounting of past theories will, therefore, serve as an introduction. 

 In addition, there is the matter of the future. But first I should like 

 to consider for a moment why it is of structure that we speak. 



A symposium on protoplasm in which structure is the chief theme 

 suggests that structure is the most significant property of living 

 matter. This is true. One may even go so far as to say that it is a 

 specific structure of matter which distinguishes the living from the 

 nonliving.^ 



The chemical composition of protoplasm is important to life. 

 Water is the dispersion medium. Salts are required to maintain 

 physical qualities. Sugars are needed for respiratory oxidations. 

 Fats serve as reserve energy. And proteins are the material out of 

 which the structural framework of living matter is made. The com- 

 position is important, but it is secondary to arrangement, to organiza- 

 tion, to structure. The proteins, for example, hold a pre-eminent 

 position among the constituents of protoplasm because they are 

 structural material. 



One may agree to the secondary position of composition and yet 

 regard emphasis on structure as arbitrary in view of the fact that 

 protoplasm is, above all, a dynamic system and not a static one. An 

 outstanding quality of living matter is activity, and activity is a 

 manifestation of energy. Energy, composition, and function are as 

 essential to a mechanism as is structure, and energy is particularly 

 significant in a living system. Indeed, one of the primary attributes 

 of life is the capacity of living matter to use energy in the synthesis 

 of protoplasm, whereas the synthesis of nonliving organic substances 

 involves the liberation of energy. 



The primary source of energy in protoplasm appears to be the 

 oxidation of carbohydrates, but this is not in itself an extraordinary 

 reaction. It is not the kind of energy but the use to which this energy 

 is put which distinguishes protoplasm; and this uniqueness of living 



'Philos. of Sci., 6:266, 1939. 



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