Ill 



head nods, and we take less notice of outward ob- 

 jects, till at length all the thoughts are iii confusion, 

 and a sort of delirium ensues, from whence there is 

 a transition to sleep, not known to us. This is has. 

 tened by darkness, composure of mind, and absence 

 of irritation from all parts of the body. 



Again, whatever weakens the natural powers, in- 

 clines to and increases sleep j such as loss of blood, 

 cooling medicines, yea the cold of the external air. 

 Add to these, whatever calls off the quantity of 

 blood flowing to the heart, as warm bathing of the 

 feet, a plentiful ingestion of food into the stomach : 

 likewise whatever lessens the motions of the spirits, 

 whether in the brain or stomach, heart, or arteries 

 On the contrary, some hot medicines induce sleep, 

 by causing a greater afflux of blood to the brain. 

 The same effect have some fevers, as also fatness, and 

 whatever else retards the venal blood. In all these 

 eases, the blood collected in the head compresses the 

 brain, so as to lessen the course of the spirits into the 

 nerves. 



Sleepiness is likewise produced by any compres- 

 sion of the brain, whether from extravasated blood, 

 a depressed part of some bones, or a collection of se- 

 rous water within the ventricles. 



Sleep therefore sometimes rises from a defect of the 

 spirits: always from a collapsing of the nervous 

 fibres, through which the spirits pass from their foun. 

 tain to all parts of the body. 



It is hindered by intense thought, pain of body, 

 and strong emotions of mind : all which urge the 

 spirits on, and prevent the nervous fibres from col- 

 lapsing. 



In sleep, the heart is gradually restored from its 

 quick and almost feverish pulsation, to its slow and 

 calm motion, the breathing is slower and smaller, the 

 motion of the stomach and intestines, the digestion 

 of the aliments, and the progression of the faeces are 

 diminished. At the same time the thinner juices 

 move more slowly, while the more gross are called 



