8 PROTOPLASM 



phosphorus, potassium, sodium, chlorine, sulphur, magnesium, 

 iron, iodine, fluorine, silicon, manganese, arsenic, etc. 



There is a tendency to regard protoplasm as a very simple 

 physical system. To be sure, it is, as a whole, primarily a phys- 

 ical mixture and not a compound in the true chemical sense. In 

 some respects, it resembles as simple a system as a solution of salt 

 or sugar in water, but it is inconceivable that living matter is no 

 more intricate than this. There is no direct optical evidence of 

 great complexity in protoplasm, but if we view the question 

 dynamically, and consider the extreme diversity in the form and 

 behavior of organisms, reflecting for a moment on the manifold 

 activities of a single cell, such as that in the brain of a man or in 

 the leaf of a tree, it would seem that protoplasm must be a highly 

 complex and superbly organized system. 



Complexity in structure leads to the question whether or not 

 this structure or any other property of protoplasm is charac- 

 teristic of it alone, i.e., of life. It is recognized that living matter 

 is in certain respects quite distinct from nonliving matter. It is 

 further recognized that a definite structural organization or 

 specific constituent of protoplasm may be responsible for this 

 distinction, but just what type of organization or particular 

 constituent cannot be said. One aspect of this problem is seen in 

 the attempts made to distinguish between what is alive and 

 what is not alive in protoplasm and to restrict the term proto- 

 plasm so that it will include the living constituents only, but all 

 such attempts are in the main futile. However, it does appear 

 justifiable to regard certain of the constituents of protoplasm, 

 such as a fat droplet, a starch grain, or a crystal, as lifeless. The 

 water, which makes up three-fourths of protoplasm, is certainly 

 not alive when considered apart as water, but some of it may be 

 so intimately associated with other constituents of protoplasm 

 as to become in a sense alive. Those protoplasmic centers where 

 metabolic activity is greatest — centers of organic synthesis such 

 as the chloroplasts where sugar is formed and the pyrenOids 

 where starch is formed — would appear to merit the title of 

 living as much as, if not more, than any other part of the cell, but 

 it is these very processes and the substances involved which are 

 capable of the strictest physical-chemical interpretation. Chlo- 

 rophyll may be viewed simply as a catalyst or merely as a color 

 screen and thus robbed of all "vital" significance. 



