DISINTEGRATION OF NERVOUS MATTER WITH USE. 239 



are not known) the amount of sleep required by different persons, for the 

 maintenance of a healthy condition of the Nervous. System, varies consider- 

 ably ; some being able to dispense with it to a degree which would be exceed- 

 ingly injurious to other individuals, who do not surpass them in mental activity. 

 Where a prolonged exertion of the mind has been made, and the natural tend- 

 ency 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 

 Nutrition 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 irregu- 

 lar manner) of the cerebral functions, and an absence of disposition to sleep. 

 Such a state may continue for some time ; 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. 



295. 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 plwsphalic deposits in the urine, and especially 

 of those having alkaline bases, 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 fol- 

 lows any temporary strain upon its powers, can scarcely be set down to any 

 other 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 

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

 is found to be almost invariably 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 premature at- 

 tempt to renew the activity of its exercise, causes the re-appearance of the 

 excessive phosphatic discharge indicative of an undue waste of nervous mat- 

 ter.* 



296. There is not the same evidence of constant change, however, in re- 

 gard to \hefibrous element of the Nervous System; and its conducting power 

 appears to be much less dependent upon the supply of blood, than is the ori- 

 ginating power of the vesicular matter. It remains, with little decrease, for 

 some time after death ; especially in cold-blooded animals ; for we can, by 

 pinching, pricking, or otherwise stimulating the motor trunks, give rise to con- 

 tractions in the muscles supplied by them, exactly as during life. Its earlier 

 departure in warm-blooded animals, may be partly due to the cooling of the 

 body. 



297. Of the actual nature of the changes by which impressions are received 

 upon the peripheral origins of the afferent nerves, or are communicated to the 



* A large amount of evidence confirmatory of the above views, and showing the im- 

 portance of carefully distinguishing between the alkaline and earthy phosphates, has been 

 adduced by Dr. Bence Jones, in a Paper lately read to the Royal Society. The quantity of 

 the latter, which is present in the urine, is found to bear a constant relation to that which is 

 contained in the food. On the other hand, the amount of the former varies with dull-rent 

 conditions of the nervous system, in such a manner as to warrant the inference that its pro- 

 duction is a result of the disintegration of nervous matter; being due to the union of the 

 phosphoric acid thus set free, with alkaline bases present in the blood in a state of feeble 

 combination. 



