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- 2 

 suit has been contradicted by other J- 

 observers,* who claim that during sleep ? 

 there is a vascular dilatation in the brain 5 

 as well as in the limbs. In view of this 

 contradiction in results between experi- | 

 menters making use of similar methods w 

 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 intb question. * 

 More extensive observations upon in- 

 dividuals with an opening in the skull- H. 

 wall are greatly needed to determine this & 

 point. The author f has extended Mos- g' 

 so's observations so as to obtain a pleth- 

 ysmographic record of the volume of the "? 

 hand and part of the forearm during H 

 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 g" 

 one and two hours after the begin- 

 ning of sleep. After this maximum g 

 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, g 

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

 Physiol. Soc."); Brodmann, "Journal f. Psychologie u. Neurologic," 1, 10, 



1902. 



t Howell, loc. cit. 



