98 THE LAWS OF ORGANIC 



CHAP. IV. 



The ^Distribution of the Blood at different Ages and 

 Seasons. 



LXXXV. WE have been long accustomed to 

 regard the circulation of the blood as composed 

 of an arterial and of a venous system, continually 

 in action ; but our attention has never yet been 

 sufficiently awakened to investigate the import- 

 ant alterations of which these systems are sus- 

 ceptible. The lungs and the heart commence 

 their functions at birth, and as long as life con- 

 tinues they perform the designs of Nature ; but 

 these designs and effects are variable, because the 

 necessities of the system change with the evolu- 

 tion of new, or the feebleness and imperfection of 

 old organs. The lungs unceasingly act upon the 

 blood, and the heart every moment conspires to 

 propel it ; but the former do not always pos- 

 sess the same capability, nor does the latter ex- 

 hibit the same energy through the different stages 

 of existence. If then the qualities of the blood 

 are modified by the different conditions of organ- 

 ization, and if its propulsion and circulation are 

 also subject to the same, is it philosophical to 

 suppose that its distribution will be equable or 

 uniform ? 



