504 THE CHEMISTRY OF CREATION. 



ated, is further propelled by the heart through- 

 out the body of the creature, and, losing its 

 oxygen in the capillary vessels, returns again 

 by the veins to undergo the same process 

 again. In so doing the venous blood parts with 

 carbonic acid, which is received and retained 

 by the surrounding fluid in a dissolved state. 

 The temperature of fishes is generally two or 

 three degrees higher than that of the water in 

 which they live. These facts render it apparent 

 that it is not less important to the residents of 

 the waters than to ourselves to be provided 

 with a full and free supply of oxygen, and ex- 

 plains the cause of the death of fish when placed 

 in a limited quantity of water, even though 

 the water may not have undergone any sen- 

 sible change. When fish are thus placed, and 

 have exhausted the stock of dissolved oxy- 

 gen in the fluid, they rise to the surface, and 

 swallow atmospheric air, the oxygen of which 

 becomes then subservient to their uses. This 

 can rarely occur in a state of nature, but it is 

 constantly seen when fish are kept in small 

 artificial receptacles. It is a most common and 

 painful sight to witness this action in gold-fish, 

 kept within the too narrow confines of a glass 

 globe. 



The effect of the respiration of fish and of 

 the presence of other marine inhabitants upon 



