596 PRACTICE OF PHYSIC. 



mal economy a tendency to observe such periods ; and the cri- 

 tical days above mentioned are consistent with this tendency of 

 the economy, as all of them mark either tertian or quartan pe- 

 riods. ^These periods, however, are not promiscuously mixed, 

 but occupy constantly their several portions in the progress of 

 the disease ; so that, from the beginning to the eleventh day, a 

 tertian period takes place ; and from the eleventh to the twen- 

 tieth, and perhaps longer, a quartan period is as steadily ob- 

 served. 



CXX. What determines the periods to be changed about 

 the eleventh day, we have not clearly perceived but the fact is 

 certain; for there is no instance of any termination on the 

 thirteenth, that is, the tertian period next following the eleventh ; 

 whereas, upon the fourteenth, seventeenth, and twentieth, which 

 mark quartan periods, there are forty-three instances of termina- 

 tions, and six only on all the intermediate days between these. 



This prevalence of a quartan period leaves no room for doubt- 

 ing that the twentieth, and not the twenty-first, is the critical 

 day marked by Hippocrates, though the last is mentioned as 

 such in the common edition of the aphorisms, taken from an 

 erroneous manuscript, which Celsus also seems to have copied. 



CXXI. A consistency with the general tendency of the sys- 

 tem renders the series of critical days we have mentioned pro- 

 bably the true one ; and the only remaining difficulty in find- 

 ing what we have delivered to be the same with the genuine 

 doctrine of Hippocrates, is the frequent mention of the fourth as 

 a critical day. 



It is true, there are more instances of terminations happen- 

 ing on this day than on some of those days we have asserted to 

 be truly critical. But its inconsistency with the more general 

 tendency, and some other considerations, lead us to deny its 

 being naturally a critical day ; and to think that the instances 

 of terminations which have really occurred on the fourth day, 

 are to be reckoned among the other irregularities that happen 

 in this matter. 



CXXI I. I have thus endeavoured to support the doctrine 

 of critical days, chiefly upon the particular facts to be found in 

 the writings of Hippocrates : and although I might also pro- 

 duce many other testimonies of both ancient and modern times, 



