584 PHILOSOPHICAL TRANSACTIONS. [aNNO 1/33. 



regularly and copiously in sleep, when all external objects cease to solicit our 

 senses, and the will no longer determines the spirits into the muscles of volun- 

 tary motion ; which two kinds of actions, as well as the operations and passions 

 of our mind, do, in the day-time, make strong derivations of the spirits from 

 the natural and vital functions; which, for tiiat reason, are never so perfect as 

 in sound and undisturbed sleep. 



Those who are acquainted with the doctrine of derivations and revulsions, 

 founded on innumerable observations in the animal economy and practice of 

 physic, know, that a flux of any of the animal fluids, arising from nature, or 

 from a disease, or provoked by art, to any one or more parts of the body, or 

 to any organ of secretion or excretion, will cause a sensible proportional dimi- 

 nution of the afflux to, and of the secretion and excretion, by the other parts 

 and organs. 



Therefore, as soon as a deficiency of animal spirits happens by labour, or 

 from any other cause whatever, that defect will be first felt in the organs of 

 sensation, the muscles of voluntary motion, and the operations of the mind ; 

 because these are not acted on by such powerful and irresistible agents, as the 

 organs of the natural and vital functions are, in perfect health ; for the mind, 

 being sensible of the defect of spirits for its actions and operations, chases to 

 forbear : we retire from external objects, and then the whole of the remaining 

 spirits are led to tlie natural and vital organs, by the mechanism above described; 

 and the organs of sensation and voluntary motion must be entirely deserted by 

 them, for that time; which is the state of sleep, and which will continue till a 

 greater quantity of spirits be recruited, than is consumed in the natural and vital 

 functions ; at which time the redundancy or overplus begins again to be secerned 

 into the other deserted nerves, viz. into those of sensation and voluntary motion ; 

 which, flowing now copiously into the relaxed muscles, excites stretching, 

 yawning, &c. and at last rouses out of sleep. 



'2. A too plentiful meal is known to cause a heaviness, inactivity, listlessness, 

 an aversion to motion or action, a drowsiness, sleepiness, and in some sleep it- 

 self, soon after eating. 



It has been proved above, that this cannot proceed from a distention of the 

 stomach ; it has also been endeavoured to prove, that in such, the lacteals are 

 never empty, and that the chyle of the preceding meal is forced througii them 

 into the blood by the succeeding, almost instantaneously, or as soon as the 

 peristaltic motion is excited or increased by the food taken down, which must 

 be during the time of such a meal, or very soon after, according to the degree 

 of fulness of the lacteals before that meal. What change then can we imagine 

 to have happened to the body, in this time of a meal, so remarkable, and so 



