CIKCULA.TTON IN THE CKANIUM. 335 



ing the activity of the brain, than during the suspension of 

 its functions in sleep. The blood-vessels of the meninges 

 were exposed freely to view by the operation, and were ex- 

 amined by the microscope, with a low power, as well as with 

 the naked eye. 1 Dr. Hammond has lately published an in- 

 teresting paper on sleep and insomnia, in which the obser- 

 vations of Mr. Durham are fully confirmed, leaving no doubt 

 that the vessels within the cranial cavity are subject to con- 

 siderable physiological variations in tension. These obser- 

 vations were published in 1865, 2 though they were made 

 before the article of Mr. Durham appeared. 



Physiologists, even before the time of Haller, had noticed 

 alternate movements of expansion and contraction in the 

 brain, connected with the acts of respiration. This is ob- 

 served in children before the fontanels are closed, and in 

 the adult when the brain is exposed by an injury or a 

 surgical operation. The movements are, an expansion with 

 the act of expiration, which, in violent efforts, is sometimes 

 so considerable as to produce protrusion, and contraction 

 with inspiration. Magendie also studied these movements, 

 which he explained in the following way : 3 With the act of 

 expiration, the flow of blood in the arteries is favored, and 

 the current in the veins is retarded. If the effort be violent, 

 the valve at the opening of the internal jugular may be 

 closed. This act would produce an expansion of the brain, 

 not from reflux by the veins, but from the fact that the flow 

 into the chest is impeded, and the blood, while passing in 

 more freely by the arteries, is momentarily confined. With 

 inspiration, the flow into the thorax is materially aided, and 

 the brain is in some degree relieved of this expanding force. 



1 ARTHUR E. DURHAM, The Physiology of Sleep. Guy's Hospital Reports, 1860, 

 p. 149. 



2 WM. A. HAMMOMD, M.D., On Sleep and Insomnia. New York Medical Jour- 

 nal, 1865, vol. i., Nos. 2 and 3. 



3 Journal de Physiologic, tome i., p. 132. De V Influence des Mouvements de la 

 Poitrine et des Efforts sur la Circulation du Sang. 



