OF VITAL MOTION. 19 



again as at first; and as the absorbing power of the 

 original centres is suspended we may argue that 

 the vessels which are most dilated at the time of 

 suspension, will in their turn take upon themselves a 

 faculty of expansion and become centres of attraction. 

 These secondary centres will expand at the expense 

 of the neighbouring vessels : and this process will go 

 on (as in the first instance) until a barrier is opposed 

 to further progress by external resistance. Cotem- 

 poraneously with the cessation of the flow of latex 

 to these points a third order of centres will be 

 established in other parts of the web where the vessels 

 are largest, and there being no impediment to their 

 enlargement, they will go on dilating, until, as in the 

 former instances, the efficient cause is balanced by 

 external resistance. A fourth order of centres will 

 succeed the third, and a fifth be superadded upon the 

 fourth, and so on in an unending series, the position 

 of the new centres in each case being in those portions 

 of the vascular web which are most dilated when the 

 old centres cease to enlarge. 



In the absorption produced by the expansion of 

 these fugitive hearts we find a cause which will tend 

 to empty all congested portions of the vascular web, 

 and by this means we may partially account for the 

 supervention of the stage of contraction upon that of 

 dilatation. A second cause may also be found in the 

 changes which have taken place in the contents of 



c2 



