23 
of the Heart and Arteries. 
traction, since the enlargement and contraction of the blood- 
vessels of a limb are well known to attend the increase or 
diminution of its muscular exertions. There is also another 
way, in which the diminution of the strength of an artery may 
increase the apparent magnitude of the pulse, that is, by di- 
minishing the velocity with which the pulsation is transmitted : 
for we have seen that the magnitude of the pulse is in the in- 
verse ratio of the length of the artery distended at once; and 
this length is proportional to the velocity of the transmission : 
but it must be observed, that the force of the pulse striking 
the finger would not be affected by such a change, except that 
it might be rendered somewhat fuller and softer, although a 
considerable throbbing might be felt in the part, from the in- 
creased distension of the temporary diameter of the artery. 
How little a muscular force is necessary for the simple trans- 
mission of a pulsation, may easily be shown by placing a finger 
on the vena saphena, and striking it with the other hand at 
a distant part ; a sensation will then be felt precisely like that 
of a weak arterial pulsation. 
The deviations from the natural state of the circulation, 
which are now to be cursorily investigated, may be either 
genera] or partial ; and the general deviations may consist 
either in a change of the motion of the heart, or of the capa- 
city of the capillary arteries. When the motion of the heart 
is affected, the quantity of blood transmitted by it may either 
remain the same as in perfect health, or be diminished, or in- 
creased. Supposing it to remain the same, the pulse, if more 
frequent, must be weaker, and if slower, it must be stronger ; 
but this latter combination is scarcely ever observable ; and in 
the former case, the heart must either never be filled, perhaps 
