FUNCTIONS OF NERVOUS TISSUE. 355 



venes after any unusual exertion of this kind. In the healthy state of the body, 

 when the exercise of the Nervous system by day does not exceed that which the 

 rejtose of the night may compensate, the nutritive operations maintain it in a 

 condition which fits it for constant moderate exercise ; but unusual demands upon 

 its activity whether by long-continued and severe exercise of the intellect, by 

 excitement of the emotions, or by the combination of both, in that state of 

 anxiety which the circumstances of man's condition too frequently induce oc- 

 casion an unusual " waste/ 7 and require a prolonged repose and uninterrupted 

 nutrition, for the complete restoration of its powers. There can be no doubt that 

 (from causes which are not known) the amount of Sleep required by different 

 persons, for the maintenance of a healthy condition of the nervous system, varies 

 considerably ; some being able to dispense with it, to a degree which would be 

 exceedingly injurious to other individuals, who do not surpass them in mental 

 activity. Where a prolonged exertion of the mind has been made, and the na- 

 tural tendency to sleep has been habitually resisted by a strong effort of the will, 

 injurious results are sure to follow. The bodily health breaks down; and too 

 frequently the mind itself is permanently enfeebled. It is obvious that the Nu- 

 trition of the nervous system becomes completely deranged; and that the tissue is 

 no longer formed, in a manner requisite for the discharge of its healthy functions. 

 The same may be said of the state of Mania \ in which there is, for a time, an 

 extraordinary degree of activity (though manifested in an irregular manner) of 

 the cerebral functions, and in absence of disposition to sleep. Such a state may 

 continue for some weeks ; but the subsequent exhaustion of nervous power is 

 proportioned to the duration of the excitement, and frequent attacks of mania 

 almost invariably subside at last into Imbecility. 



361. Additional evidence for the belief that the functional activity of the 

 Nervous tissue involves disintegration of its tissue by the agency of Oxygen, is 

 found in the increase of alkaline phosphates in the urine, when there has been 

 any unusual demand upon the nervous power. No others of the soft tissues 

 contain any large amount of phosphorus ; and the marked increase in these 

 deposits, which has been continually observed to accompany long-continued wear 

 of mind (whether by intellectual exertion, or by the excitement of the feelings), 

 and which follows any temporary strain upon its powers, may fairly be attributed 

 to this cause. The most satisfactory proof is to be found in cases in which there 

 is a periodical demand upon the mental powers ; as, for example, among Clergy- 

 men, in the preparation for and discharge of their Sunday duties. This, when 

 the demand for mental exertion is severe, and especially when there is that state 

 of excitability of the nervous system which is frequently coexistent with a dimi- 

 nution of its vigor, is found to be very commonly followed by the appearance of 

 a large quantity of the alkaline phosphates in the urine. And in cases in which 

 constant and severe intellectual exertion has impaired the nutrition of the brain, 

 and has consequently weakened the mental power, it is found that any prema- 

 ture attempt to renew the activity of its exercise, causes the reappearance of the 

 excessive phosphatic discharge, indicative of an undue "waste" of nervous 

 matter. 1 Further, it has been shown by Dr. Bence Jones, 2 that acute affections 

 of nervous substance, both organic and functional, are generally attended with 

 an increase in the phosphatic salts of the urine ; the amount of phosphates, in 

 acute inflammation of the brain, seeming to be proportional to the intensity of 

 the inflammation, and in various forms of disordered action (delirium tremens, 



1 The Author has known more than one case of this kind, occurring among young men 

 whose anxiety for distinction had induced them to go through an excessive amount of intel- 

 lectual labor during their Student-life, and who found themselves forced to pay the penalty 

 of that excess, in a subsequent prolonged abstinence from all mental occupation involving 

 the slightest degree of effort. 



2 "Philosophical Transactions," 1846. 



