316 PROGRESS OF SCIENCE IN THE CENTURY. 



often full of granules. But they had little idea of 

 the intricate complexity of the cell-substance, which 

 Virchow has lived to realise and in part to eluci- 

 date. Perhaps it is to Briicke (1861) that we should 

 trace back the beginning of the recognition that the 

 cell-substance is anything but homogeneous, any- 

 thing but like white of egg. We have elsewhere * 

 sketched some of the steps which led to our present 

 realisation of the complexity of the cell-substance, 

 which some compare to a network, others to a 

 tangled coil of fibrils, others to a gelatinous matrix 

 with embedded granules, and others to a foam or 

 emulsion. It seems probable enough that one and 

 the same cell-substance may at different times ex- 

 hibit different complexities of structure. But the 

 important fact is the one, to which more perfect 

 lenses, more rapidly acting fixatives and subtler stain- 

 ing re-agents have led modern workers, that the cell 

 has a complex structural organisation. 



What is meant by Protoplasm. The term proto- 

 plasm, which Huxley defined as " the physical basis 

 of life," is often used topographically to include the 

 whole of the physically complex cell-substance. It 

 is also employed as the equivalent of cytoplasm; 

 i.e., for the complex cell-substance minus the nucleus. 

 In another usage it means the whole cell-substance in 

 so far as that is actively concerned in vital processes, 

 that is to say, the cell-substance minus obviously life- 

 less inclusions (metaplasm). There are some again 

 who try to confine the term to designate the genu- 

 inely living stuff, and this would be most convenient 

 were it not for the unhappy fact that we are at 

 present unable to isolate that genuinely living stuff, 

 or even to be sure that there is any one stuff that 

 * The Science of Life, 1899, Chap. IX. 



