FEVERS. 593 



most heedless observer may not perceive such paroxysms, and 

 though in the advanced state of the disease they are more ob- 

 scure, we cannot doubt of their existence. I before took notice 

 of the fact, with respect to intermittents, that when they 

 seem to be at an end, yet there is some cause lurking in the 

 system which gives a constant tendency to the repetition ; and 

 that on those days which would have been the days of the 

 paroxysm, had the disease constantly appeared without inter- 

 missions. Hence that particular rule of Celsus, that the pa- 

 tient ought to be attentive to the days upon which the fever 

 would have returned, lest any trespass in the non-naturals should 

 bring it on again. And we are readily led to believe, that 

 where fevers are of the most continued kind, there is still a ten- 

 dency to the same periods, which we see the system is con- 

 stantly disposed to follow." 



CX. These considerations render it probable that exact pe- 

 riodical movements may take place in continued fevers ; and I 

 think there is evidence of such movements actually taking 

 place. 



CXI. The critical days, or those on which we suppose the 

 termination of continued fevers especially to happen, are, the 

 third, fifth, seventh, ninth, eleventh, fourteenth, seventeenth, 

 and twentieth. We mark none beyond this last ; because, 

 though fevers are sometimes protracted beyond this period, it is, 

 however, more rarely ; so that there are not a sufficient number 

 of observations to ascertain the course of them ; and further, 

 because it is probable that, in fevers long protracted, the move- 

 ments become less exact and regular, and therefore less easily 

 observed. 



CXI I. That the days now mentioned are the critical days, 

 seems to be proved by the particular facts which are found in 

 the writings of Hippocrates. From these facts, as collected 

 from the several writings of that author by M. De Haen, it ap- 

 pears, that of one hundred and sixty-three instances of the ter- 

 mination of fevers, which happened on one or other of the first 

 twenty days of the disease, there are one hundred and seven, or 

 more than two-thirds of the whole number, which happened on 

 one or other of the eight days above mentioned ; that none hap- 

 pened on the second or thirteenth day ; and upon the eighth, 



