GENERAL CONDITIONS OF BRAIN-ACTIVITT. 97 



dredths of a second shorter on cold winter days (Vintscligau 

 apud Exner, Hermann's Hdbli., p. 270). 



Intoxicants alter the time. Coffee and tea ajDjDear to 

 shorten it. Small doses of ivine and alcohol first shorten and 

 then lengthen it ; but the shortening stage tends to disap- 

 pear if a large dose be given immediately. This, at least, 

 is the report of two German observers. Dr. J. W. Warren, 

 whose observations are more thorough than any previous 

 ones, could find no very decided effects from ordinary doses 

 (Journal of Physiology, viii. 311). 3IorpMa lengthens the 

 time. Amyl-nitrite lengthens it, but after the inhalation it 

 may fall to less than the normal. Ether and chloroform 

 lengthen it (for authorities, etc., see Buccola, j). 189). 



Certain diseased states naturally lengthen the time. 



The hypnotic trance has no constant effect, sometimes 

 shortening and sometimes lengthening it (Hall, Mind, viii. 

 170 ; James, Proc. Am. Soc. for Psych. Research, 246). 



The time taken to inhibit a movement (e.g. to cease con- 

 traction of jaw-muscles) seems to be about the same as to 

 produce one (Gad, Archiv f. (Anat. u.) Phvsiol., 1887, 468 ; 

 Orchansky, ihid., 1889, 1885). 



An immense amount of work has been done on reaction- 

 time, of which I have cited but a small pai't. It is a sort 

 of work which appeals particularly to patient and exact 

 .minds, and they have not failed to profit by the opportunity. 



CEREBRAL BLOOD-SUPPLY. 



The next point to occuj^y our attention is the changes of 

 circulation which accompany cerebral activity. 



All parts of the cortex, when electrically excited, produce 

 alterations both of respiration and circulation. The blood- 

 pressure rises, as a rule, all over the body, no matter where 

 the cortical irritation is applied, though the motor zone is 

 the most sensitive region for the purpose. Elsewhere the 

 current must be strong enough for an epileptic attack to be 

 produced.* Slowing and quickening of the heart are also 

 observed, and are independent of the vaso-constrictive 

 phenomenon. Mosso, using his ingenious 'plethysmo- 



* Fran9ois-Franck, Fonctions Motrices, Le^on xxn. 



