CHAPTER II 

 THE FUNDAMENTAL PHYSIOLOGICAL ACTIONS 



The Properties of the Living Body. Just as the structure of 

 the Body is the sum total of the structures of its individual cells, 

 so the properties, or functions, of the Body are the sum total of the 

 functions of the constituent tissues. With most of the properties 

 of our Bodies we are familiar in a general way. The ability to per- 

 ceive sensations and to make motions; the beating of the heart, the 

 movements of breathing, the secretion of saliva and of sweat, the 

 maintenance of bodily warmth; all these we recognize as bodily 

 functions. The power of performing them must reside with the 

 constituent cells. We observe, however, that in our Bodies not 

 all these properties are shared equally by all the cells. The cells 

 that perceive sensations are not the same as perform active move- 

 ments; those that secrete saliva have not the power of secreting 

 sweat. A Body in which a large degree of specialization prevails 

 we speak of as highly organized. In the simpler animals there is 

 less specialization and we find individual cells doing more than one 

 kind of work. In the simplest animals of all, the one-celled ani- 

 mals, all the properties possessed are necessarily combined in a 

 single cell. We can observe, then, in the rudimentary form, to be 

 sure, in the one-celled animals, all the fundamental properties of 

 living protoplasm. Chief among these are: (1) assimilation, the 

 power to take in food materials and to make them over into body 

 substance; a typical one-celled animal, the ameba, can be observed 

 under the microscope engulfing and dissolving in its own proto- 

 plasm minute food particles; (2) active motion, seen in all save a 

 very few animal forms from the lowest to the highest. Motion in 

 animals is brought about by forcible contractions of the moving 

 parts; the property of motion is therefore more accurately de- 

 scribed as contractility; (3) sensation, excitability, or irritability, the 

 property of being affected by changes in the environment; (4) co- 

 ordination, the power of causing all the parts of the organism to 

 act in harmony; (5) reproduction, the property of separating off a 



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