A STUDY IN MORBID AND NORMAL PHYSIOLOGY. 



153 



at first some slight rise in the pressure, as is shown in the tracing (Plate II. Fi*^. 5). 

 The arterial pressure was watched for nearly twenty nuuutes after the destruction 

 of the brain and suffered no notable fall; showing that nothing comparable to a 

 governing vaso-motor centre had been destroyed. 



The experiments of the series are on the whole so closely concordant tliat 

 further repetition has seemed unnecessary. They appear to establish the following 

 conclusions: After section of the vaiji, in the cnrarized animal, inild irritation of the 

 Eitzifs rerjion has no influence vpon the Hood pressure; but the application of 

 jpowerful galvanic currents or of great mechanical violence produces a more or less 

 marked elevation of the arterial pressure, which probably is due not to irritation 

 of the Hitzig's region itself, but to irritation of the trigeminal nerve twigs in the 

 dura mater, by diffusion of the electric current or of the excessive mechanical 

 force.* Total destruction of the Hitzifs region in hoth sides of the brain does 7ioi 

 abate the blood lyressure. 



The conclusions, just reached, would seem to show tliat neither irritation nor 

 destruction of the first cerebral convolution in the dog is able distinctly to afi'ect 

 the arterial pressure when the par vagum is cut and the splanchnic nerves are 

 entire. 



Such experiments arc however not entirely satisfactory. It is conceivable that 

 a vaso-motor centre, controlling the bloodvessels in the muscles, may exist in the 

 upper cerebrum and give no unmistakable sign of its presrnce when it is destroyed, 

 because it is so overshadowed by the abdominal vaso-motov system; just as the 

 addition of an individual dollar could not be perceived in a heap of coin. To sift 

 the matter as closely as possible, several furtlicr series of experiments were undi-r- 

 taken. In the first of these, a sensitive nerve w-as galvanized, after section of the 

 splanchnics and destruction of Hitzig's region in the cerebral cortex. It has 

 already been shown that when the Hitzig's region is intact and the splanchnics are 

 divided, galvanization of the sciatic causes a decided rise of the arterial pressure; 

 now if this rise does not occur after destruction of tlie Hitzig's centre, such centre 

 must obviously have a vaso-motor value; on tiie other hand, if the rise occur after 

 as before the destruction of the cerebral cortex, the vaso-motor value of the latter 

 must be null or exceedingly unimportant. 



In the second series of experiments Hitzig's region was destroyed after section 

 of the splanchnics, and the eftcct upon the arterial system noted. 



If, after removal of the disturbing influence of the powerful abdominal circula- 

 tion, the Hitzig's cortex is unable to sensibly influence the arterial pressure, i. c, 

 the vaso-motor condition of the extra-abdominal bloodvessels, the ascribing of a 

 dominant vaso-motor power to it seems more than gratuitous. The experiments are 

 as follows : — 



* I have frequently uoterl signs ot extreme paiu when working with brain uienibranes never 

 any when the brain itself was alone disturbed. 



20 July, 1330. 



