592 PRACTICE OF PHYSIC. 



thing in the nature of fevers which generally determines them 

 to be of a certain duration ; and therefore that their termina- 

 tions, whether salutary or fatal, happen at certain periods of the 

 disease rather- than at others. These periods are called the 

 Critical Days ; carefully marked by Hippocrates and other an- 

 cient physicians, as well as by many moderns of the greatest 

 eminence in practice ; while at the same time many other mod- 

 erns, of no inconsiderable authority, deny their taking place in 

 the fevers of these northern regions which we inhabit. 



CVIII. I am of opinion that the doctrine of the ancients, 

 and particularly that of Hippocrates, on this subject, was well 

 founded ; and that it is applicable to the fevers of our climate. 



CIX. I am of this opinion, first, Because I observe that 

 the animal economy, both from its own constitution, and from 

 habits which are easily produced in it, is readily subjected to 

 periodical movements. Secondly, Because, in the diseases of 

 the human body, I observe periodical movements to take place 

 with great constancy and exactness ; as in the case of intermit- 

 tent fevers, and many other diseases. 



" Nothing is more obvious than that the animal economy is 

 subject to periodical habits, and that we are of a nature which is 

 easily affected by custom and habit. The animal economy is ex- 

 posed to certain causes recurring regularly to act upon it; these 

 in a body so disposed, therefore, must actually produce such 

 periodical movements : and further, we know that in fact they 

 do take place in our ordinary health, in the business of sleep, 

 appetite, and excretions ; and that particularly in many diseases 

 they are distinctly to be observed, as in the various Intermit- 

 tents. Let us take but the single instance of a quartan, which 

 for the space of six months will return every fourth day, and 

 that at stated hours as exactly as the clock strikes. In the 

 smallpox, measles, epilepsy, asthma, &c. we have occasion to 

 observe the same exactness in the recurrence of the paroxysms 

 or of their periodical movements. I would say that they occur 

 particularly in continued fevers, from this consideration, that 

 many of these do arise from intermittents in the manner I 

 before explained, by shortening the intervals more and more 

 till they come not only to a daily paroxysm, but to a paroxysm 

 twice a-day ; and there are few continued fevers in which the 





