560 OF DEATH. 



the blood, affects the brain. This disturbance may be brought on in 

 many ways, as by the pressure of the stomach after a hearty supper, or 

 in diseased conditions, such as hydrothorax ; but it is popularly supposed, 

 where these morbid conditions are not obviously concerned, to be attrib- 

 uted to sleeping on the back. Though- this is undoubtedly true in a 

 great many instances, it is very far from being an essential condition, for 

 nightmare may occur in any position that the sleeper may possibly as- 

 sume. The restraint upon the arterialization of the blood, which appears 

 to be its essential condition, interferes with the circulation through the 

 lungs on the principles that have been described in a preceding chapter, 

 nor can the heart force a passage, however violently it may throb. The 

 effect depends not so much upon the apparent rate and power with which 

 the respiration is going on, for any embarrassment or difficulty in the in- 

 troduction of air merely leads to snoring, which is in no manner connected 

 with nightmare. The cause of this latter affection is to be sought for in 

 the air-cells, which are unable to rid themselves, with their accustomed 

 facility, of the carbonic acid and other effete products of respiration which 

 they contain. 



2D. OF DEATH. 



At all periods of life, the functional activity of the system occasions a 

 Condition of waste ^ ^ s tissues by the interstitial death of their parts, and 

 healthy equi- therefore involves a necessity of repair. So long as the repa- 

 ration balances the waste, a healthy equilibrium is maintained ; 

 but when the nutritive powers decline, as old age approaches, a gradual 

 deterioration of the system ensues. 



The period of greatest activity is also that of greatest waste, and of 

 the most active and perfect repair, interstitial death and the removal of 

 decayed material then occurring in the most rapid manner. The energy 

 of life is thus dependent on the amount and completeness of death. 



At a later period, with advancing years, although the loss of substance 

 through functional activity may be lessened, the renewal and restoration 

 of the portions which are necessarily consumed are far more than corre- 

 spondingly diminished. We thus become incapacitated corporeally and 

 mentally, and, if no accident intervenes, we die through mere old age. 



On several occasions we have already noticed the analogy between the 

 Death of a ^ Q f individuals and that of species. An analogy also may 

 molecule, of an "j^ traced in the circumstances and causes of their death, for 



individual or-,-. ,, 1111 11 t 



ganism,ofa the discoveries of geology abundantly show that thousands 

 species. O f sp ec i es j n the organic series have become extinct. The 



death of a constituent molecule in an animal body, the death of the in- 

 dividual animal itself, the death of the species to which it belongs, are 

 all philosophical facts of the same kind, though presenting, perhaps, in 



