THE PHYSICAL CHEMISTRY OF PROTOPLASM 223 



process, abnormal reactions take place, and the factory output is 

 interrupted. 



No other conception than this one of a definite structure and 

 coordination of the different working parts of a cell can adequately 

 account for the great variety of chemical changes which are 

 constantly going on in any given cell. It is wholly inconceivable 

 that a homogeneous mass of all the varying chemical compounds 

 which are contained in any given quantity of protoplasm could 

 either exist or produce any regular sequence of chemical reactions. 

 Structure, or organization of the cell-contents into separate col- 

 loidal compartments, and the segregation of cell-contents into 

 masses having different functions, is essential to any reasonable 

 conception of how the cell performs its various activities. 



The best understanding of the structural arrangement is 

 afforded by the conception that protoplasm consists of a colloidal 

 gel, or sometimes a very viscid sol, containing water, salts, carbo- 

 hydrates, fats, proteins, and enzymes. Evidence in favor of this 

 conception is afforded by the appearance of protoplasm under a 

 high-power microscope, and by the close resemblance of the 

 processes which go on in it, and its responses to external stimuli, 

 to those of an artificial gel of similar chemical composition. 



Two different conceptions of the form in which the chemical 

 components exist in this mass have been advanced. One is that 

 they are in true molecular unions, known as " biogens," and that 

 the reactions which take place in the mass may, therefore, be 

 studied from the same basis as are reactions between similar sub- 

 stances when they take place in a beaker or test tube in the 

 laboratory. It would seem, however, that the constantly varying 

 proportions of the materials themselves, and the lack of homo- 

 geneity of cell contents, afford insurmountable difficulties to this 

 conception as a basis for the study of cell activities. The other, 

 and seemingly more reasonable, conception is that these bodies 

 exist in the form of colloidal complexes, whose composition 

 may vary within wide limits and whose reactions are responsive to 

 the usual phenomena incident to the colloidal condition of matter. 



According to the latter conception, vital activities of cell 

 protoplasm may be due to changes in water content, to electrical 

 disturbances, to the phenomena resulting from the cqnditions 

 brought about by surface boundaries between the different phases 

 of the gel, to varying osmotic pressure, to changes in chemical 



