*9 
of the Heart and Arteries. 
a very slight excess of force can be found to carry it on, or 
when the blood which they contain finds a readier passage 
than usual, by means of their communication with such parts 
as are now deprived of their natural supply. 
It is difficult to determine, whether blushing is more pro- 
bably effected by a constriction or by a relaxation of the 
vessels concerned ; it must, however, be chiefly an affection 
of the smaller vessels, since the larger ones do not contain a 
sufficient quantity of blood to produce so sudden an effect. 
Perhaps the capillary vessels are dilated, while the arteries, 
which are a little larger only, are contracted : possibly too an 
obstruction may exist at the point of junction of the arteries 
with the veins ; and where the blush is preceded by paleness, 
such an obstruction is probably the principal cause of the 
whole affection. 
With respect to the tendency of inflammation in general to 
extend itself to the neighbouring parts, it is scarcely possible 
to form any reasonable conjecture that can lead to its expla- 
nation : this circumstance appears to be placed beyond the 
reach of any mechanical theory, and to belong rather to some 
mutual communication of the functions of the nervous system, 
since it is not inflammation only, that is thus propagated, but 
a variety of other local affections of a specific nature, which 
are usually complicated with inflammation, although they may 
perhaps, in some cases, be independent of it. Inflammations, 
however, are certainly capable of great diversity in their na- 
ture, and it is not to be expected, that any mechanical theory 
can do more than to afford a probable explanation of the most 
material circumstances, which are common to all the different 
species. 
