32 PATHOLOGY. 



an impression upon the nervous system as to cause the action 

 of the heart to be much increased, such increase being entirely 

 consistent with a state of perfect healtli in an animal so cir- 

 cumstanced. 



The relation between the pulse and respiratory movements, 

 with the exception above mentioned, is generally maintained 

 where the pulse and respirations are naturally accelerated, as 

 after exercise; but in disease it generally ceases to exist. 

 In many diseases accompanied by increased frequency of the 

 pulse, the acceleration of the respiratory movements bears 

 no comparison to the increased number of the pulsations, and in 

 many other cases the respiration may be very rapid without a 

 proportionate increase in the number of the pulsations ; in some 

 instances the pulse may actually fall below its normal standard, 

 whilst the respirations are increased. 



The natural pulse of the horse beats about forty times a minute, 

 that of the cow about from forty to fifty, with the exceptions 

 already mentioned, and the pulse of the dog ranges from eighty 

 to one hundred, depending upon the size and breed of the animal, 

 and the pulse of the sheep from seventy to eighty. 



The frequency of the pulsations, and the regularity and 

 irregularity of their succession, depends wpon the heart, and the 

 pulse at the jaw and arm, when it can be felt, always corre- 

 sponds to the contraction (systole) of the ventricles, allowance 

 being made for the very slight interval that must elapse before 

 the wave of blood reaches these parts. To the heart's action 

 must also be referred most of the healthy conditions as well as 

 many of the peculiarities in disease ; but the vital condition of 

 the arterial system is not without its influence on the character 

 of the pulse. 



The arteries are gifted with a certain amount of vital contrac- 

 tility or tone, given to them by their muscular coat, upon which 

 their healthy firnmess depends ; without this tone they become 

 relaxed and flaccid, yielding readily to the force of the wave of 

 blood, and but slowly recovering their calibre when the expand- 

 ing wave has passed onwards. It is evident that, in this con- 

 dition of the vessels, a portion of the impulse of the heart, 

 which is expended in dilating the arteries, is not restored to the 

 blood by the contraction of their coats ; the impulse being thus 

 gradually diminished as the arterial wave proceeds on its course, 



