RATIDITY OF THE CIRCULATION. 



75 



The action of the heart may be taken as a general index of tbjs. The following 

 table has been drawn up from the researches of Dumas, Prevost, Midler, and Simon. 



Rapidity of Circulation in Different Animals. 



Tbis table shows that the rapidity of the circulation corresponds with the struc- 

 ture, habits, age, and development of animals. 



If the vital forces are of a low grade, either from original conformation or the 

 depressing influences of old age, the circulation is correspondingly sluggish and 

 feeble. 



As tbe fluids and solids of animals become more highly elaborated and developed, 

 the action of the heart and circulation of the blood become more rapid and vigorous. 



The next consideration is that of the structure of the respiratory system in the 

 different orders of animals. 



One of the essential conditions of the life of all organized beings, whether vege- 

 table or animal, is a supply of oxygen. The modes in which oxygen is brought 

 in contact with the fluids and solids of organized structures, vary with the develop- 

 ment and peculiar manner of life of the different classes of animals. 



In the lowest classes of the Invertebrata, in which the digested matters pass 

 directly from the stomach into the different structures of the body, and become 

 integral parts of the animal, we find no special circulatory system, and respiration 



