164 PHYSIOLOGY. 



CLXXII. The frequency of the systole of the heart will be 

 more or less, 1. As the blood in the veins is more or less 

 quickly returned to either ventricle of the heart. 2. As the 

 ventricles of the heart are more or less entirely evacuated at 

 each systole. 3. As the muscular fibres of the heart are more 

 or less moveable. 4. As the action of the nervous and ani- 

 mal powers are more or less increased with respect to the 

 heart. 



CLXXIII. As the arteries of a healthy body are always 

 full, the blood thrown out of the ventricles into the arteries 

 during the systole of the heart, can only find a place there by 

 pushing on the blood with the velocity (CLXIX.), or by di- 

 lating the arteries ; but as the resistances (CLXX.) prevent 

 the blood from flowing with the velocity (CLXIX.), the blood 

 thrown out of the heart must, in some measure, dilate the ar- 

 teries, and thereby form what is called the PULSE. 



CLXXIV. It appears, that, in the arteries, to a certain 

 length, the blood moves faster during the systole than during 

 the diastole of the heart ; but, as the resistances and causes of 

 retardation become greater in every portion of the arteries as 

 it is more distant from the heart, so the acceleration of the 

 blood during the systole of the heart ' must be greater in any 

 portion of the arteries nearer the heart than in the next adjoin- 

 ing that is more distant ; and, so far as this takes place, a dila- 

 tation of the arteries will happen, even from a small quantity of 

 blood thrown out of the ventricles. 



CLXXV. As the resistances to the blood's motion in the 

 blood-vessels increase with the distance from the heart, there 

 may be a part of the sanguiferous system in which the motion 

 of the blood will not be accelerated during the systole of the 

 heart, and in which, therefore, no pulse can be discerned. This 

 happens in the extreme branches of the aorta ; and no pulse is 

 ever observed in the extreme branches of the vena cava. 



CLXX VI. The velocity and impetus of the blood, in the 

 whole system of blood-vessels, will always be as the action of the 

 heart and arteries taken together. 



CLXX VII. The velocity and impetus of the blood, in 

 any particular part of the system, will be, 1. As the part is 

 more or less distant from the heart. 2. As the circumstances 



