CHAPTER VI. 



THE GENERAL ANIMAL FUNCTIONS, AND THEIR 

 APPROPRIATE ORGANS. 



85. Protoplasmic Functions. It has already been stated 

 that in protoplasm reside the fundamental powers belonging 

 to living things. Through its agency all the metabolic or 

 assimilative 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. 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 products which are to be eliminated. The power of 

 receiving and responding to surrounding influences, which we 

 have called irritability and contractility, is likewise a power 

 of protoplasm. Out of these arises the possibility of organ- 

 isms 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 consider- 

 able localization. 



86. Division of Labor. As the protoplasmic units, i. e., 

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

 masses, they 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 its own substance, 

 but we find certain activities largely given over to special 

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

 contractility in some, and irritability in others. This division 

 of labor, is accompanied by a corresponding differentiation of 



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