The Excitable Cortex of tlie Chimpanzee, Orang-Utan, and Gorilla 215 



The thickness of the wall of the parietal bone overlying the thermo- 

 meter bulb was 3 ram. in fresh state, i.e. about the same thickness as of an 

 ordinary human skull in tliat region. Also a certain amount of temporalis 

 muscle intervened between the scalp and bone at the place of application 

 of the bag. 



The above instances are representative of the results obtained in the 

 short series of observations made. The chimpanzee used in the above 

 observations was chosen because, from previous operations on the other 

 hemisphere, it was recognised to have a skull of more than average 

 thickness. 



From the above, it is seen that by local application of cold and warmth 

 to the scalp under conditions similar to their application clinically in man 

 the temperature at the cortex of the underlying brain may be varied 

 readily over a range of about 10° F. (e.g. 91-5° F.-101-5° F.). 



VIII. Effect on the Excitability of the Motor Cortex of 



CLOSING THE CaROTID ArTERIES. 



We have observed upon six chimpanzees the effect of closure of the carotid 

 arteries upon the excitability to faradism of the hand, leg, and face areas 

 of the cortex. In three of these simultaneous closing of the two common 

 carotid arteries extinguished the excitability of the cortex. In one of the 

 three animals the excitability of the cortex lapsed in 100 seconds in the 

 right motor area and in 115 seconds in the left, after simultaneous closure 

 of both carotids. The vessels were then released, and the excitability, 

 as tested in hand area, returned in 75 seconds in left hemisphere and in 



