302 SCIENCE PROGRESS 



what the word itself implies in ordinary language, a little box 

 or capsule, a small space enclosed in firm walls. But with 

 increased knowledge it became apparent that the fluid contents 

 were the essential living part of the cell and that the cell-wall 

 was of secondary importance, merely an adaptive product of 

 the contained living substance or protoplasm. Hence the word 

 "cell," as used in biology, underwent a complete change in its 

 connotation and came to have a meaning altogether different 

 from that which the word has in common speech, often very 

 puzzling to those unacquainted with the technicalities of the 

 biological sciences, the cell being defined simply as a small 

 mass or corpuscle of the living substance which might either 

 surround itself with a cell-wall — the product of its own secretive 

 activity — or remain naked and without any protective envelope. 

 With still further advance in knowledge, it was found that in 

 every cell entering into the structure of an ordinary plant or 

 animal there was present at least one body of peculiar pro- 

 perties which was termed the nucleus ; on account of its 

 universal occurrence, as well as the peculiar relations it was 

 found to bear to the life of the organism, this body soon came 

 to be regarded as an essential component of the cell. Thus we 

 arrive at last at the now generally accepted definition of the cell : 

 a vital unit consisting of an individualised mass of the living 

 substance protoplasm containing at least one nucleus. 



We are arrived, then, at this point, that the unit-masses of 

 the living substance of which the bodies of ordinary animals and 

 plants are built up are themselves composed of at least two 

 essential parts. Using the term "protoplasm" for the living 

 substance as a whole, we can assert that the protoplasm of an 

 ordinary cell is differentiated into two distinct components, the 

 cytoplasm or body-protoplasm and the nucleus. Here at once 

 the question arises, is this differentiation of the protoplasm a 

 primary characteristic of the living substance which was ex- 

 hibited by our hypothetical primum vivens or is it a differentiation 

 which was acquired in the course of evolution ? If the latter 

 alternative be the true one, is the nucleus or is the cytoplasm 

 the more primitive constituent of the living substance or are 

 they both to be regarded as derivatives of a substance yet more 

 primitive? For my part, I cannot conceive that the earliest 

 living creature could have come into existence as a complete 

 cell, with nucleus and cytoplasm distinct and separate ; I am 



