Cell and Protoplasm. 113 



structure has suggested which is of physiological inter- 

 est. The idea is, that a cell consists of a relatively 

 stable living framework, and of a changeful content 

 enclosed by it. Prof. Burdon Sanderson expresses it 

 thus: "The framework is the acting part, which lives 

 and is stable; the content is the acted-on part, which 

 has never lived and is labile, that is, in a state of 

 metabolism or chemical transformation". This view 

 naturally leads those who adopt it to regard protoplasm 

 as a sort of ferment acting on less complex material 

 which is brought within its sphere of influence. It is 

 the strange characteristic of a ferment that it can act on 

 other substances without being itself affected by the 

 changes which it produces, and that it can go on doing 

 so continuously with a power which has no direct rela- 

 tion to its amount. In these respects a ferment is sug- 

 gestive of what many suppose living matter to be. We 

 may note, however, that to credit the framework with 

 essential vitality and to regard the interstitial content as 

 merely material is an assumption, comparable to that 

 which exalts the chromatin of the nucleus and depreciates 

 the achromatin. 



Another certain fact is, that the functioning of cells is 

 often demonstrably accompanied by marked changes in 

 the physical appearance of the cell-structure. Relatively 

 simple illustrations are furnished by glandular cells, like 

 those of the pancreas, as described by Heidenhain and 

 others; more difficult instances are the structural changes 

 of nerve-cells after prolonged function, as demonstrated 

 by Hodge, Mann, and others. There is no doubt that a 

 considerable area in the cell is often affected by vital 

 function, and this might be called the protoplasmic area. 

 In such facts, at least, a basis might be found for 

 another conception of protoplasm, that it is itself the 

 seat of constant change, that it is constantly being 

 unmade and remade, that it is the central term in a 

 metabolic series. Thus Prof. Michael Foster speaks 

 of protoplasm as if it occupied the summit of a set 

 of chemical staircases. On the one hand, there is an 

 ascending series of assimilative or constructive chemical 

 steps, with each of which the material taken in as food 



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