18 OF VITAL MOTION. 



operation of organic heat. Where indeed a vessel is 

 more dilated, there we may suppose molecular changes, 

 which will necessitate a further dilatation, by which 

 additional quantities of fluid will be attracted from 

 neighbouring parts; for although changes take place 

 cotemporaneously in vessels which are contracted and 

 comparatively empty, yet these lesser phenomena will 

 be absorbed and counteracted by the greater. For the 

 same reason, also, that the more expanded portions 

 should, in the first instance, be the seat of a more 

 vigorous extrication of heat and consequent expansion, 

 by which currents are determined towards them, so 

 also we must grant the possession of the same faculty 

 when they have become more expanded by absorption. 

 Once set up indeed, the process of expansion must go 

 on in these parts, for anything we know to the con- 

 trary, either until a sufficient resistance is opposed 

 by the pressure of neighbouring parts, or until the 

 vessel is ruptured for the coats will be less able to 

 resist the distending force as the expansion progresses. 

 The stage of contraction in the laticiferous web 

 which supervenes upon dilatation would seem to argue 

 the abstraction or suspension of force, and such may 

 be the case. This will appear if we leave those focal 

 centres which have attained their maximum degree of 

 enlargement, and cast our eyes upon other portions of 

 the same system of vessels. There we find irregularity 

 in the sizes of the tubes : and hence we may begin 



