300 CIRCULATION [Lesson xx xix 



power could produce j yet whose continuation 

 requires the constant aid of the same hand that 

 first gave it existence. The brain transmits ani- 

 mal spirits to the heart, to give it a vigorous con- 

 traction. The heart, at the same time, pushes 

 the Blood into the brain to supply it with new 

 spirits; by which means the head and the heart 

 give continual mutual support to each other. But 

 this is not all ; the action of the heart sends the 

 Blood and other vital humours over the whole body 

 by the arteries, and distributes nourishment and 

 rigour to every part (while perhaps the animal 

 spirits, from the extremities of the nerves, return 

 again into the Blood), and the whole refluent mass 

 is conveyed back through the veins into the heart, 

 which enables it, without intermission, to persi&t 

 in rolling this tide of li/e. 



But here it must not be supposed, that the arte- 

 ries pass on to the extremities of the limbs, before 

 they communicate wivh the returning veins : for 

 upon this supposition, after an amputation has 

 been performed, whatever Blood might be brought 

 to the stump by the arteries, it is certain, none of 

 it could be carried back again to ihe heart; be- 

 cause the intercourse between the heart and the 

 limbs would, in this case, be entirely cut off. But 

 the all-wise AUTHOR of our being has provided for 

 this exigency, by forming a great number of less 

 branches from the larger arteries, which constantly 

 communicate with corresponding branches of 

 the rturning veins. And hence, it is easy to 



conceive 



