58 ANIMAL INDIVIDUALITY [CH. 



as it builds itself up and breaks itself down, the 

 unstable intermediate substance, nitrosylsulphonic 

 acid, must continually make, unmake, and remake 

 itself. As long as the raw materials are present in 

 the right proportions, the reaction will go on in- 

 definitely. So it is with protoplasm : the conditions 

 under which the inorganic reaction can take place 

 are merely more restricted, so that for it to continue, 

 man must step in with elaborate mechanisms to 

 ensure adequate supplies of the substances concerned, 

 provision for their due mixing, care for the removal 

 of their by-products. 



Any machinery that protoplasm makes for facili- 

 tating its reactions it must not only make itself, but 

 actually out of itself. So it comes about that any 

 improvement in working must mean some change in 

 the structure of the protoplasm, and since improve- 

 ment usually means division of labour, improved 

 working brings with it a visible differentiation of 

 parts in the previously homogeneous cell. What 

 was a cell and nothing more is now a cell and an 

 individual to boot. 



Our primitive homogeneous masses of protoplasm, 

 though all the evidence leads us to assume them, are 

 purely hypothetical. Every cell that we know to-day 

 contains at least three, and probably more, diverse 

 and mutually helpful substances. There is the outer 

 layer, whose primary function is absorption, though 



