510 PRACTICE OF PHYSIC. 



hours, shew that our body is subject to a diurnal revolution 

 steadily and regularly. But in none of the functions is this 

 revolution more remarkable and more regular than in that of 

 the pulse, as may be seen from Dr. Bryan Robinson's Observa- 

 tions. When a man first awakens out of sleep, suppose he 

 be free from any disease, his pulse is at the slowest ; but he 

 has no sooner stirred a little, than it becomes quicker, and con- 

 tinues to be so during the forenoon. And this quickness is not 

 altogether owing to exercise, &c. for although this be used, or 

 stimuli applied, instead of farther increasing in frequency the 

 pulse decreases about noon : then it rises in the afternoon about 

 dinner time ; but, in spite of stimuli, diet, and all the irritations 

 the system is exposed to during all this time, it suffers a remis- 

 sion about seven or eight o'clock ; then it suffers another exa- 

 cerbation, and continues to increase till midnight, when it rises 

 higher than ever; remitting again from about two o'clock in the 

 morning, till it arrives at its state of greatest slowness in the 

 morning. But there is hardly a function in the animal econo- 

 my which is not a proof that our system, by a certain law or 

 habit, is subject to diurnal revolutions.' 1 



LVI. It is this diurnal revolution, which, I suppose, deter- 

 mines the duration of the paroxysms of fevers ; and the con- 

 stant and universal limitation of these paroxysms (as observed 

 in LV.), while no other cause of it can be assigned, renders it 

 sufficiently probable that their duration depends upon, and is 

 determined by, the revolution mentioned. And that these par- 

 oxysms are connected with that diurnal revolution, appears fur- 

 ther from this, that though the intervals of paroxysms arc 

 different in different cases, yet the times of the accession of 

 paroxysms are generally fixed to one time of the day ; so that 

 quotidians come on in the morning, tertians at noon, and quar- 

 tans in the afternoon. 



LVI I. It remains to be remarked, that as quartans and ter- 

 tians are apt to become quotidians, these to pass into the state 

 of remittents, and these last to become continued ; and that 

 even in the continued form, daily exacerbations and remissions 

 are generally to be observed ; so all this shows so much the 

 power of diurnal revolution, that when in certain cases the daily 

 exacerbations and remissions are with difficulty distinguished, we 



