THE PHYSICAL CHEMISTRY OF PROTOPLASM 237 



SUMMARY 



It is evident that, within the limits of a single chapter, it has 

 been possible to give only a very brief and incomplete discussion of 

 some of the most important applications of the principles of phys- 

 ical chemistry to the properties and activities of protoplasm. 

 Therefore, it may be profitable to summarize briefly these into a 

 series of definite statements which may serve as a review of the 

 principles which have been discussed in the preceding chapters, as 

 applied to the activities of protoplasm. 



Protoplasm is a complex hydrogel, composed of an heterogeneous 

 mixture of proteins, fats, and carbohydrates, arranged in a foam- 

 ,like structure, the compartments of the gel being filled with an 

 aqueous solution of the soluble organic products of synthesis and 

 of varying proportions of mineral salts which are of the same gen- 

 eral nature as those of sea-water. 



The gel is hot uniform throughout the volume of any given cell, 

 but is differentiated in different parts into what are known as the 

 nucleus, the chloroplasts, the plasma of the cell, etc. 



The vital activities of the cell consist in chemical reactions 

 which are controlled by comparatively slight changes in the elec- 

 trolyte distribution, or other environmental changes which affect 

 the colloidal condition of the mass and, generally speaking, result 

 in changes of the water content of the plasma, most such chemical 

 changes being essentially reversible hydrolytic reactions. 



The components of active protoplasm are in a condition most 

 favorable to chemical reactions by reason of the enormous surface 

 area of the colloidal material, resulting in abundance of available 

 energy, intimate contact of the reacting materials, and the nearest 

 possible approach to the condition of true solution which can be 

 obtained without the loss of stable form and structure. 



The reactions which take place in cell protoplasm, as a result 

 of the action of either physical or chemical stimuli, are accom- 

 panied by electrical disturbances, which may be either caused by, 

 or the result of, changes in the electrical charges of the mineral 

 salts which are present in the gel. Such changes, like the chem- 

 ical reactions which they accompany, may be regarded as rever- 

 sible and mutually self-regulatory; so that the protoplasm has 

 not only the possibilities of enormous chemical reactivity, but also 

 the mechanism for self-regulation of its actions, the products or 



