EXPRESSION OF SLEEP. 227 



of profound unconsciousness, as a rule, no reflex 

 movements follow impressions on the organs of 

 sense. 



We are considering, at present, expression in 

 healthy subjects only, and the only normal con- 

 dition of unconsciousness is sleep. We pass on 

 by a natural step to study the objective signs of 

 sleep. Sleep is a condition apt to follow from 

 fatigue. The principal signs of sleep are, diminished 

 impressionability, diminished power to resist the 

 effects of gravity upon the postures of the body, 

 absence of movements in the so-called voluntary 

 muscles, alteration of the organic movements. 

 Many details might be given, a few must suffice 

 for want of space. The tone of the orbicular 

 muscle of the eye is, in healthful sleep, sufficient 

 to keep the eyelids closed ; on awaking, the levator 

 muscle of the upper lid preponderates, and the 

 eyelid is raised. If during deep sleep the upper 

 eyelids be raised, the pupils are seen minutely con- 

 tracted, and in infants we usually see a complete 

 loss of the associated movements of the eyes.* 

 One eye may move upwards or outwards while 

 the other remains quiet, or moves in a different 

 direction, or at a different pace, thus causing a 

 temporary squint. Usually these movements are 

 confined to the horizontal plane of the axes of the 

 orbits ; at the moment o waking the pupils dilate, 

 and co-ordination of the movements of the eyes 

 is restored. I have frequently observed these facts 

 in infants asleep in their mothers' arms. It is also 

 * See paper, BritMt Medical Journal, March 10, 1877. 



