SECTION VI 



SUPPLY OF NOURISHING MATERIAL TO THE BLOOD AND LYMPH, 

 AND ELIMINATION OF WASTE MATTER FROM THEM 



I. KESPIRATION 



IF an animal be placed in a closed chamber filled with 

 ordinary atmospheric air which contains by volume 79 parts 

 of nitrogen and 21 parts of oxygen, and if the air be examined 

 after a time, it will be found that the oxygen has diminished 

 in amount, and that a nearly corresponding amount of carbon 

 dioxide has been added. (Practical Physiology.} 



The same thing occurs in aquatic animals the water round 

 them loses oxygen and gains carbon dioxide. An animal takes 

 up oxygen and gives off carbon dioxide. This is the process 

 of external respiration. 



A. EXTERNAL RESPIRATION 

 I. Respiratory Mechanism 



In aquatic animals the mechanism by which this process is 

 carried on is a gill or gills. Each consists of a process from 

 the surface covered by a very thin layer of integument, just 

 below which is a tuft of capillary blood vessels. The oxygen 

 passes from the water to the blood ; the carbon dioxide from 

 the blood to the water. 



A lung is simply a gill or mass of gills, turned outside in, 

 with air instead of water outside the integument. While in 

 aquatic gill-bearing animals there is constantly a fresh supply 

 of water passing over the gills, in lung-bearing animals the 

 air in the lung sacs must be exchanged by some mechanical 

 contrivance. 



The lungs consist of myriads of small thin-walled sacs 

 attached round the funnel-like expansions in which the air 

 passages (infundibular passages) terminate. (The structure 



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