MECHANICS OF RESPIRATION 



fulfilled. Many aquariums are thus arranged ; the com- 

 plete, constant renewal of the water without disturbance 

 of the fishes being provided for simply in this manner. 

 But there is one drawback to such a method. It calls 

 for a large quantity of water and a canalized system of 

 feeding which is not always practicable. So, the main 

 necessity being to provide oxygen at a sufficient rate of 

 solution, use is often made of systems which allow of the 

 maintenance of this proportion at the appropriate degree 

 while controlling the total output. The simplest con- 

 sists of making the water fall from above, or of forcing 

 it to spread out in a thin sheet, so as to bring it more into 

 contact with the air, extending the surface so as to 

 produce a solution of oxygen in the highest possible 

 proportion. Then the water in the tanks, being so 

 much more richly provided, is better able to satisfy the 

 needs of respiration. 



Another and more elaborate process, often employed, 

 is that of an air sprinkler. It is to be seen in well- 

 equipped aquariums. From one corner of each tank 

 there rises a jet of small air bubbles which go up to the 

 surface, losing their oxygen by solution as they do so. 

 This train of bubbles comes out of a pipe, in which the 

 water, issuing in a fine jet under fairly strong pressure, 

 carries along air, stirs it up, pulverizes it in fine bubbles, 

 then passes out into the tank with it. By this means, 

 a small quantity of water is enabled to keep alive and 

 to support a large number of creatures. The final stage 

 in this process consists in injecting air under pressure, 

 so as to replace by new oxygen that which continual 

 respiration is using up all the time, using the same 

 water, which is changed only at infrequent intervals, 

 when the fouling caused by waste products has become 

 too marked. 



These various arrangements to ensure adequate normal 



respiration to a number of creatures shut up in a confined 



space, and to give them in this respect the same degree of 



ease that they possess in the state of freedom, is suitable 



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