OF THE FUNCTIONS OF ORGANS AND TISSUES. 65 



modification of adipose tissue known as medulla or 

 marrow. 



lOO. Of tlie functions of Organs and Tissues. — Tlie 



functions or offices discliarged by organs and tissues 

 have been di\T.ded into two great classes, the animal, 

 and the organic or vegetative functions. The one 

 class is characteristic of the higher animals only, but 

 the other is common to all living things. This divi- 

 sion, however, is not strictly accurate, for, in man 

 and the higher animals, the so-called vegetative func- 

 tions could not be performed, if the so-called organs 

 of animal hfe did not act properly. The animal and 

 organic functions of the higher animals are mutually 

 dependent, and cannot strictly be regarded as be- 

 longing to separate systems. The so-called animal 

 functions comprise. Locomotion, Innervation, and 

 Special Sense. The vegetative functions so widely 

 distributed, comprise Digestion, Ahsmj^tion, Circula- 

 tion, Respiration, Secretion, Generation, and Develop- 

 ment, and the development of Heat, Light, and Elec- 

 tricity. In the lowest organisms, some of the most im- 

 portant vegetative functions are performed tlu-ough the 

 instrumentality of the general sui-face ; while in man 

 and the higher animals a separate organ is set apart 

 for the performance of each function. If I was con- 

 sideiing these different functions, I should commence 

 with the functions of organic life inH;he order in 

 which I have enumerated them, for this seems the 

 most natural mode of arrangement. First of all, the 

 food is introduced into the organism, and after being 

 altered by certain preliminary processes, is subjected 

 to Digestion, by which it is rendered soluble, and fitted 

 for the next process, that of Absorption. By this 

 the nutritive material is taken up and introduced 

 into the blood, and ultimately becomes converted into 

 blood. Thus we come to the consideration of the 

 function of Circulation; and as we foUow the blood 



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