GENEEAL DISTUEBANCE OF THE CIECULATION. 339 



with the condition of rest or activity of the whole body, or of 

 the particular organ which is the subject of observation." 



GENEEAL DISTUEBANCE OF THE CIECULATION. 



From the universal distribution of blood over the system, 

 and the manner in which movement, respiration, secretion, 

 and absorption must influence the current of blood, it is evident 

 that there are physical reasons for very frequent and sudden 

 changes in the condition of the circulation. Exertion, the 

 different positions the body may be placed in, feeding, influ- 

 ence the blood's flow; but the heart and even blood-vessels 

 are affected by causes which operate through the nervous 

 system. Any disease of important organs, and capable of 

 giving rise to constitutional disturbance, at once affects the 

 state of the circulation. The current may be retarded or 

 accelerated, and this both locally and generally. So readily 

 and certainly does the blood's flow indicate the normal or 

 abnormal state of an animal, that it is universally regarded 

 as one great criterion to test the degree of deviations from 

 health, and watch the progress of disease. 



The pulse is produced, as we have already shown, by 

 the propulsion of blood into the arteries. These vessels 

 become distended, elongate, and are, to a certain extent, 

 raised by the jerk transmitted with every heart-beat. It 

 must be remembered that there can be no pulse without con- 

 traction of the heart, and the number of pulsations per 

 minute may be determined alike in all parts of the circulatory 

 system. It is true that in distant arteries of limbs, head, 

 &c., there is a perceptible lapse of time after the con- 

 traction of the heart, which is required for the transmission 

 of the blood-wave. But, though we can determine the 

 number of pulsations by feeling the heart or arteries, the 

 character of the pulse, which is so sure a guide in determin- 



