i io The Science of Life. 



mise; (b) the ciliated Infusorians, which are usually 

 smaller, express a relative predominance of active ex- 

 penditure; and (c) the encysted parasitic Sporozoa repre- 

 sent an extreme of sluggish passivity. 



The conception is of value as an attempt to get below 

 the final results of selection to the fundamental possi- 

 bilities of form and function which supplied the raw 

 material for adaptation. 



To the earlier observers, from Dujardin and Von 

 structure of Mohl to Virchow and Max Schultze, the cell- 

 the U c e n r - e substance appeared to be a homogeneous, 

 substance. v i sc id substance, including, indeed, granules 

 and vacuoles, but still essentially structureless. 



This was a natural view with the means and methods 

 then available. But if modern work has made anything 

 certain, it is that the cell-substance has a complex 

 structure essentially different from that of a homo- 

 geneous substance like white of egg. This conclusion 

 has been arrived at partly (and most securely) by 

 observation of living cells with highly perfected (apo- 

 chromatic) lenses, partly (and less securely) by using 

 fixing reagents which kill instantaneously, and stains 

 which differentiate part from part. 



One of the first to maintain that the cell must have 

 a more complex structure than was usually supposed 

 was Brucke, who, in 1861, advanced a hypothesis of 

 minute units intermediate between the molecule and the 

 cell, an idea which has been frequently re-expressed 

 since that date. 



From Briicke, as starting-point, we might trace, 

 through Cienkowsky, Hanstein, and others, the gradual 

 growth of the conviction that the physical basis of life 

 is essentially complex in structure. It is enough, 

 however, to note that it soon began to be recognized 

 that the cell-substance consisted of a relatively stable 

 framework (spongioplasm, reticulum, &c.), and a more 

 liquid or labile ground -substance (enchylema, cyto- 

 lymph, &c.). Some, like Leydig and Schafer, main- 

 tained the greater vital importance of the ground- 

 substance, while the majority emphasized the claims of 

 the framework a question still beyond solution, 



