CHAPTER VI 



THE GENERAL ANIMAL FUNCTIONS, AND THEIR APPROPRIATE 



ORGANS 



88. Protoplasmic Functions. — It has already been stated 

 that in protoplasm reside the fundamental powers belonging to 

 living things. Through its agency all the vital processes are 

 performed. Through the activity of its ferments, foods undergo 

 changes that prepare them to be used in the manufacture of 

 protoplasm and other complex cell-substances. It alone has the 

 power to assimilate or build up these foods into the living state. 

 In protoplasm occur the oxidation and other chemical changes 

 which result in the manifestation of energy, as heat, motion, 

 light, etc., accompanied by the formation of waste produpts 

 which are to be eliminated. The power of receiving and 

 responding to surrounding influences, which we have called irrita- 

 bility and contractility, is likewise a power of protoplasm. Out of 

 these powers arises the possibility of organisms becoming 

 adapted to their surroundings. It is not yet possible certainly 

 to localize all these functions within the individual cell, although 

 it seems probable that in some degree even such protoplasm as 

 is found in the Amoeba has localized functions. In many single- 

 celled animals there is a considerable localization. 



89. Division of Labor. — As the protoplasmic units, i.e., the 

 cells, increase in number by cell division and form large masses, 

 the different cells are no longer subjected to the same influences, 

 and are not equally favorably situated for the performance of 

 all the original functions. The protoplasm of all cells retains 

 the power of using food and of building up their own substance, 

 but we find certain activities largely given over to special groups 

 of cells; e. g., secretion is specially noticeable in some, contrac- 

 tility in some, and irritability in others. This division of labor, 

 is accompanied by a corresponding differentiation of structure 

 which constitutes an adaptation to the special work to be done, 



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