28 EVOLUTION AND ANIMAL LIFE 



elementary substance other than occurs in the inorganic world. 

 These elements are combined in protoplasm into certain most 

 extremely complex compounds, which are always present where 

 life is, and never elsewhere, and hence the essential chemical 

 characteristic of living matter is the presence of these complex 

 as yet unanalyzed, albuminous compounds. 



It is obvious that this chemical half-knowledge of proto- 

 plasm makes no satisfying revelation to us explanatory of the 

 qualities of this life stuff. How is it then with the physical 

 structure of protoplasm? We know that many simple chemical 

 substances put together in particular physical relationship to 

 each other will give a capacity of performance or function quite 

 different from and beyond that which they possess when simply 

 brought together without definite order or arrangement. Is 

 protoplasm a machine with a capacity for doing extraordi- 

 nary things, with its powers due primarily to its physical 

 make-up? Unfortunately we have no satisfying answer to this 

 question. While chemists are balked in their analysis of the 

 protoplasmic make-up by the complexity of the compounds 

 they meet, a complexity too much for their present technic to 

 resolve, physicists are similarly balked in their attempt to re- 

 solve and expose the ultimate physical structure of protoplasm. 



This ultimate structure of protoplasm is ultramicroscopic, 

 and its study is checked by the limitations of microscopes. 

 When we examine protoplasm with the highest powers of the 

 microscope we see plainly that it is not as it appears under lower 

 powers, structureless and homogeneous. On the contrary it 

 reveals an apparent granular or fibrillar or alveolar or reticu- 

 lar structure. We find that protoplasm varies in its physical 

 make-up at different times or in different cells. We also find 

 that the difficulties of interpreting just what one sees when using 

 the highest microscopic powers make it impossible to be really 

 certain of understanding what is seen. But however various 

 our interpretations of the finer structure of protoplasm, they 

 agree that any bit of protoplasm is a viscous colloidal mass 

 composed of at least two substances of somewhat different phys- 

 ical make-up. One of these substances is evidently denser than 

 the other and is arranged in the form of grains, rods, threads, 

 or droplets scattered through a ground mass. Concerning this 

 dimorphic condition of protoplasm practically all biologists are 

 agreed. The names, hyaloplasm, paraplasm, or others of sim- 



