CHAPTER XVI 

 THE PHYSICAL CHEMISTRY OF PROTOPLASM 



THUS far, we have considered the chemical nature of the various 

 groups of compounds which are found in the tissues of living 

 organisms, laying emphasis upon those which are of plant origin. 

 These compounds constitute the material, or machinery, of the 

 cell, and then* various transformations furnish the energy for its 

 operation. We come now to a study of the mode of its operation, 

 or the processes of vital phenomena. 



Our knowledge of these matters is not yet far enough advanced 

 to permit a definite statement as to whether there is any difference 

 between the protoplasm of plant tissues and that of animal origin 

 in their modes of action, or in the physical-chemical changes which 

 constitute the vital phenomena in the two groups of living organ- 

 isms. Thus far, no such differences have been discovered. Hence, 

 in the following discussions, no attempt is made to differentiate 

 between animal and plant protoplasm. Most of the facts and 

 principles which are here presented have been developed as the 

 result of the study of the physiological chemistry of animal life. 

 No similar careful study of plant chemistry has yet been carried 

 out; but preliminary studies seem to indicate that the same gen- 

 eral principles apply to all protoplasm, regardless of whether it is 

 of plant or of animal origin. It is possible, of course, that further 

 studies of plant protoplasm will render necessary some modifica- 

 tions of some of these views as applied to the growth of plants; 

 but they are believed to represent the best which is now known of 

 the physical chemistry of the plant-cell activities. 



HETEROGENEOUS STRUCTURE OF THE CELL 



Examination of cell protoplasm under the microscope reveals 

 that it is not a simple homogeneous mass. In the first place, it 



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