2 34 THE POPULAR SCIENCE MONTHLY. 



this. The position of the sleeping person is often changed uncon- 

 sciously when uneasy, and the feet, when chilled, will be drawn 

 under the bedclothes. He mentions still more impressive facts, 

 such as sleeping on horseback, without danger of losing seat, once 

 the habit is acquired. We may add that men sleep leaning 

 against a wall or a tree, or even astride of a limb, without serious 

 risk of falling. Monkeys, opossums, and other animals sleep hung 

 up by helices formed of their tails. Somnambulism may be re- 

 ferred to the same class of facts. 



Prof. Michael Foster, of the University of Cambridge, Eng- 

 land, a very eminent physiologist, says, in a work published in 

 1891, that although the phenomena of sleep are largely confined 

 to the central nervous system, and especially to the hemispheres 

 of the brain, the whole body shares in the condition. " The pulse 

 and breathing are slower. The intake of oxygen and the output 

 of carbon dioxide, especially the latter, are lessened. Indeed, the 

 whole metabolism" (by which term he designates generally the 

 chemical transformations in the living organism) " and the depend- 

 ent temperature of the body are lowered." (The latter statement 

 is not in accord with other authors.) "We can not say as yet 

 how far these are the indirect results of the condition of the nerv- 

 ous system, or how far they indicate a partial slumbering of the 

 several tissues." Prof. Foster distinctly declines to enter into 

 what he calls "the psychology of sleep and dreams." But to 

 ignore dreams and their essential relations to natural sleep sug- 

 gests to the present writer the play of Hamlet with the Prince of 

 Denmark left out. 



Foster points out tl;ie fact, as the result of all experience, that 

 the recumbent posture is highly promotive of natural sleep, and 

 connects it with the reduction of energy consumed in the circula- 

 tion, especially with the large diminution of work that falls upon 

 the heart. The most remarkable and significant statements made 

 by this high authority are that " during sleep the pupil is con- 

 stricted, during deep sleep exceedingly so, and dilatation, often 

 unaccompanied by any visible movements of the limbs or body, 

 takes place when any sensitive surface is stimulated ; and on 

 awaking, the pupils also dilate." He adds that this " contraction 

 of the pupils is worthy of notice, since it shows that the condition 

 of sleep is not merely the simple and direct result of the falling 

 away of afferent " (external) " impulses. When the eyes are closed 

 in slumber, the pupils ought, since the retina is then quiescent, to 

 dilate ; that they are constricted, the more so the deeper the sleep, 

 shows that important actions in the brain are taking place." In 

 other words, as we have already set forth, certain inherent func- 

 tions of the brain, also of the nervous system, emotional and im- 

 aginative processes, among others, independent of what he calls 



