52 INTRODUCTION 



structure of colloidal solutions that they produce in the proto- 

 plasm of cells hardened by them. Neither are the appearances 

 seen in unfixed specimens reliable indications of the true struc- 

 ture of the living protoplasm. Granules of secretion may 

 disappear after or during the death of the cell (e. g., glyco- 

 gen) or they may swell up (e. g., mucin granules) thus giving 

 the appearance of a network or honeycomb which is then 

 incorrectly ascribed to the protoplasm itself. Death of the 

 cells, even when not produced by external influences, seems 

 to be accompanied by coagulation of some parts of the cell con- 

 stituents, and hence a cell examined in anything but its normal 

 living condition, an extremely difficult matter, will not present 

 a true idea of how it appears and is composed while in that 

 condition. 



If, with these facts in mind, we consider the theories of 

 morphologists as to the finer structure of the cell protoplasm 

 based upon studies of cells fixed in various hardening agents, 

 it becomes evident that the possibility that the " foam structure" 

 advocated by Biitschli, or the " thread/' " reticular, " and 

 " pseudo-alveolar " structures of Fromann, Arnold, Reinke, and 

 others, are all simply the effect of fixatives upon colloid solutions 

 seems very real. The objection always advanced to these 

 theories of protoplasmic structure, namely, that the structures 

 described were artificial productions, not present in the normal 

 living cell, and variously described and interpreted by different 

 investigators because each worked with a different hardening 

 fluid or different technic, is strongly supported by these obser- 

 vations upon colloids. The possibility that the living proto- 

 plasm is homogeneous still remains open. This matter will 

 receive further consideration in the next section. 



THE STRUCTURE OF THE CELL IN RELATION TO ITS 



CHEMISTRY AND PHYSICS 



It is obviously impossible to separate nuclei, nucleoli, 

 cytoplasm, and cell membranes from each other and to isolate 

 them in quantities sufficient for analysis, and therefore we are 

 still quite uncertain as to just the chemical differences that exist 

 between them. That there are differences is certain, and by 

 means of micro-chemical reactions, by comparing analyses of 

 cells in which nucleus or cytoplasm predominate, and by study- 

 ing their physico-chemical relations to one another, we have 

 arrived at more or less tangible ideas on the question of 

 the relation of the structural elements of the cell to its 

 composition. 



