05 THE FUNCTIONS OF THE HEART AND ARTERIES. } I7 



ue cannot hesitate to attribute the change to its permanent 

 contraction, since the enlargement and contraction of the 

 blood vessels of a limb are well known to attend the in- 

 crease 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 diminishing the velocity with which the 

 pulsation is transmitted : for we have seen, that the magni- 

 tude of the pulse is in the inverse 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 throb- 

 bing might be felt in the part, from the hici-eased disten- 

 sion of the temporary diameter of the artery. How little a Muscular 

 muscular force is necessary for the simple transmission of a ^^''^e not re- 

 pulsation may easily be shown, by placing a finger on the SapSsSon, 

 vpna saphena, and striking it with the other hand at a dis- 

 tant part ; a sensation will then be felt precisely like that of 

 a weak arterial pulsation. 



The deviations from the natural state of the circulation, Deyiations 



which are now to be cursorily investigated, may be either ^'■°'" *^^ "^\"* 

 , , , 1 . . . ral state of the 



general or partial ; and the general deviations may consist circulation, 



either in a change of the motion of the heart, or of the ca- 

 pacity of the capillary arteries. When the motion of the when the mo- 

 heart is affected, the quantity of blood transmitted by ittionofthe 

 may either remain the same as in perfect health, or be di-^d*^ 

 minished, or increased. 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 ei- 

 iher never be filled, perhaps on account of too great irrita- 

 bility, or never be emptied, from the weakness of its mus- 

 cular powers. But the immediate effect of such a change 

 as this, in the functions depending on the circulation, can- 

 not be very material, and it can only be considered as an 

 indication of a derangement in the nervous and muscular 

 system, which is not likely to lead to any disease of the vital 

 functions. When the quantity of blood transmitted by the 



feeart 



