270 PHYSIOLOGY OF CENTRAL NERVOUS SYSTEM. 



suggestion, the sleep of hypnotism, has been studied by means 

 of the plethysmographic method.* The result, so far as the 

 volume of the arm and hand is concerned, shows that in this con- 

 dition, unlike normal sleep, there is a marked diminution in 

 volume, and, therefore, we may believe, an increased constriction 

 of the blood-vessels of the skin. This observation accords with 

 the blanched appearance of the skin of the extremities, and with 

 the statement that in deep hypnotic sleep the skin does not bleed 

 readily when pricked with a needle. In view of our limited knowl- 

 edge, however, it would be hazardous to base any comparison 

 between normal and hypnotic sleep upon this single fact. Some 

 authors,! in fact, doubt whether there is a true hypnotic sleep. 

 They incline to the view that the immobilization or diminished 

 excitability produced by hypnotic suggestion or manipulation 

 simply passes into a condition of natural sleep. 



* Walden, "American Journal of Physiology," 4, 124, 1900-01. 

 t Pi6ron, loc. tit. 



