CHAPTER XV 



THE STRUCTURE OF PROTOPLASM AND 

 ORGANIC COLLOIDAL MATTER 



The structure of protoplasm is one of the essentially physical 

 qualities of living matter, comparable to elasticity, viscosity, 

 and those other qualities that we have just been considering. 

 It is, therefore, rightly grouped with these similar physical 

 properties, yet for a complete understanding of it many facts 

 to be considered later are necessary. We must decide between 



Fig. 114. — The coarse protoplasmic emulsion as seen in the egg of Fucus. 



continuity in subject matter and the anticipation of much that 

 is to come. We select the former and suggest that this chapter 

 be reread after completing the book, not only for a better under- 

 standing of it but also because theories on the structure of proto- 

 plasm represent the culmination of all our knowledge of living 

 matter. 



THE VISIBLE STRUCTURE OF PROTOPLASM 



Theories on the structure of protoplasm fall into two catego- 

 ries—those having to do with the microscopically visible structure 

 and those dealing with the structure that lies beyond the visible. 

 The first is based on direct observation; the second, on interpreta- 



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