CHAPTER V. 



ON THB ABSOKPTION AND CIRCULATION OF FOOD IN 

 PLANTS AND ANIMALS. 



The vegetative functions of nutrition and reproduction, 

 have for their principal object the support of life in the 

 different individuals, and the multiplication and propaga- 

 tion of their species. 



Nutrition is undoubtedly the most important and general 

 of the functions of animal and vegetable life. It operates 

 in a continuous manner, commencing with life and ceasing 

 only at its termination, whilst the other functions manifest 

 themselves only under certain conditions, and at determinate 

 epochs. 



Nutrition in plants and animals is a very complicated 

 function, and implies several distinct acts : 1. The intro- 

 duction of food into the interior of the organism, {absorp- 

 tion.) 2. Its distribution to all its-^parts, (circulation.') 

 3. The elaboration of the nutritive fluid by contact with 

 the air, {respiration.) 4. Its conversion into the substance 

 of the organism, {assimilation.) 5. The elimination of such 

 matters as are not necessary, {excretion.) 



ABSOEPTION IN PLANTS AND ANIMALS. 



Before food can enter the tissues of any organized 

 being, whether animal or plant, it must be reduced to a 

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