THE PHYSIOLOGY OF SLEEP. 



263 



blood, while a smaller amount flows to the brain. The volume of 

 the foot or hand was measured in these experiments by incasing 

 it in a plethysmograph (see section 

 on Circulation) . Unfortunately, this re- 

 sult has been contradicted by other 

 observers,* who claim that during sleep 

 there is a vascular dilatation in the brain 

 as well as in the limbs. In view of this 

 contradiction in results between experi- 

 menters making use of similar methods 

 of work, it is evident that theories, such 

 as are described below, which^are based 

 upon a diminution in blood-flow through 

 the brain, are brought into question. 

 More extensive observations upon in- 

 dividuals with an opening in the skull- 

 wall are greatly needed to determine this 

 point. The author f has extended Mos- 

 so's observations so as to obtain a pleth- 

 ysmographic record of the volume of the 

 hand and part of the forearm during 

 a period of normal sleep. One of the 

 records thus obtained is given in Fig. 

 116. The amount of dilatation is 

 given by the ordinates below the base 

 line. Granting that the increase in 

 volume of the hand and arm is caused 

 by an increase in the volume of blood 

 contained in their blood-vessels, the 

 curve shows that during and after 

 the onset of sleep the blood-vessels in 

 the arm slowly dilate until between 

 one and two hours after the begin- 

 ning of sleep. After this maximum 

 is reached the arm remains more or 

 less of the same volume for a certain 

 period or else diminishes in volume 

 very gradually. Shortly before waking, 

 however, the arm begins to diminish 

 more rapidly in size, owing, doubtless, 

 to the contraction of its blood-vessels; 

 so that at the time of awaking it has practically the same volume as 

 at the beginning of sleep. If, on the basis of Mosso's experiments, 



* Shepard, 



Physiol. Soc."); Brodmann, "Journal f 

 1902. 



American Journal of Physiology," 23, 1909 ("Proc. Amer. 

 . Psychologie u. Neurologic, " 1, 10, 

 t Howell, loc. cit. 



