230 THE POPULAR SCIENCE MONTHLY. 



placed. It can not be pressed into the spinal canal, for the latter cav- 

 ity is already tensely full. 



Referring to the classical essay of Dr. Kelly * for experimental 

 proof of the difficulty of affecting the mass of intra-cranial blood, I 

 content myself here with a single argument, looking at the subject 

 from a common-sense point of view. 



Whatever opinion may be held as to the nature of nervous energy, 

 the phraseology used when its discharge is spoken of implies a certain 

 amount of stress in the nerve-center. Thus, "vibration" can not oc- 

 cur without tension, and " explosion " implies previous repression. A 

 chord will not give a clear tone when it is relaxed ; and, if the cham- 

 ber in which a cartridge is exploded is not perfectly rigid, the effect 

 on the bullet is weakened. If we are at liberty to reason from analo- 

 gies like these, we must infer that no nerve-center can have its energy 

 economically liberated unless its structure is subjected to a certain 

 amount of stress. Now, stress in a nerve-center means stress in its 

 circulation, and this involves pressure outward and equally in every 

 direction. If the energy is to be liberated with ease, and with exact- 

 ness as to amount and direction, support to the structures immediately 

 concerned must be as little yielding as possible. But if the cerebro- 

 spinal fluid is at liberty to flow and ebb as readily as some writers as- 

 sert, this steady support would be absent. The brain in such a case 

 would resemble an instrument with slackened strings, and would re- 

 fuse to give a clear response to impressions. Sudden or powerful or 

 exact voluntary effort would then be simply impossible. For here, as 

 everywhere, the discharge of pent-up energy will take place in the 

 direction of least resistance. If the displacement of the organ's sup- 

 port occur more readily than the production of the intended result, 

 such as the movement of a limb, the latter will not be successfully 

 accomplished. Some of the energy would be wasted in the form of 

 simple mechanical effect on the surroundings, and the result, whether 

 mental or motor, will be less precise than would otherwise be the 

 case. 



The inference, then, is obvious. If time be an essential factor in 

 the production of any change in the bulk of the brain-tissue, or in that 

 of the cerebro-spinal fluid, then for the time being the mass of intra- 

 cranial blood must also remain a stable quantity. 



If we are allowed to assume the correctness of our last postulate, 

 two corollaries require to be kept in view in applying it to encephalic 

 physiology. In the first place, no change can take place in the circu- 

 lation of one portion of the brain without that of some other part 

 being inversely affected. In the abdomen, a determination of blood 

 to one organ need not of necessity involve a diminished supply to 

 the rest of the cavity, but an analogous occurrence within the skull is 



* "Transactions of the Medico-Chirurgical Society of Edinburgh," vol. i. 



