CHAPTER V 



THE FUNDAMENTAL, LIVING SUBSTANCE- 

 PROTOPLASM 



Difficult to Comprehend 



Living substance — protoplasm — appears to be a difficult con- 

 cept for the uninitiated to comprehend. "Living" things 

 are all about us, but ordinarily we do not see protoplasm — what 

 we do see is the lifeless external skin, or covering, of an animal, 

 or the equally lifeless bark of a tree or other coverings of vege- 

 table life, all formed through the activities of protoplasm, but 

 not themselves the living protoplasm. With the microscope, 

 however, it is possible to see and to study not only living things 

 as organisms but also the protoplasm of which they are com- 

 posed. This is particularly illuminating when observed in the 

 smallest living unicellular organisms. So far as size is concerned, 

 it must be clearly understood that many multicellular animals 

 (Metazoa) and many multicellular plants (Metaphyta) are 

 microscopic, but the limits of the present volume forbid a dis- 

 cussion of these. 



A Typical Cell 



A typical cell* is made up of protoplasm and its derivatives, 

 and, structurally, consists of a cell body (cytoplasm) and a dif- 

 ferentiated portion called the nucleus. The cytoplasm contains 

 inclusions of many kinds, some of which, known as plastids (e.g., 

 chloroplastids, pyrenoids, etc.), are functional in protoplasmic 

 activities, i.e., they perform some of the life processes,'*' whereas 

 others, known as metaplastids, are products of protoplasmic ac- 

 tivity (starch, paramylum,* fats, oils, etc.), and play but a 

 passive role in the life of the cell. 



* See "The Coming and Evolution of Life," page 8, and "The Plant World," 

 pages 5 and 34, both in this Series. 



t See "The Coming and Evolution of Life," page 7, in this Series. 

 I Paramylum is a carbohydrate, allied to starch. 



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