946 GENERATION. 



"We do not propose to consider, in this connection, the psychological variations which 

 occur at different ages, but, as regards the general process of nutrition, it may be stated, 

 in general terms, that the appropriation of new matter is a little superior to disassimila- 

 tion up to about the age of twenty-five years ; between twenty -five and forty -five, these 

 two processes are nearly equal ; and, at a later period, the nutrition does not completely 

 supply the physiological waste of the tissues, the proportion of organic to inorganic 

 matter gradually diminishes, and death follows, as an inevitable consequence of life. In 

 old age, the muscular movements gradually become feeble ; the bones contain an excess 

 of inorganic matter ; the ligaments become stiff ; the special senses are usually obtuse ; 

 and there is a diminished capacity for mental labor, with more or less loss of the memory 

 and of intellectual vigor. It is a curious fact that remote events are more clearly and 

 easily recalled to the mind in old age, than those of recent occurrence ; and, indeed, 

 early impressions and prejudices then appear to be unusually strong. 



It frequently happens, in old age, that some organ essential to life gives way, and that 

 this is the immediate cause of death ; or that an old person is stricken down by some 

 disease to which his age renders him peculiarly liable. It is so infrequent to observe a 

 perfectly physiological life, continuing throughout the successive ages of man, that it is 

 almost impossible to present a picture of physiological death ; but we sometimes observe 

 a gradual fading away of vitality in old persons, who die without being affected with any 

 special disease. It is also difficult to fix the natural period of human life. Some per- 

 sons die, apparently of old age, at seventy, and it is rare that life is preserved beyond 

 one hundred years. In treating of the so-called vital point, we have stated that there 

 does not seem to be any such occurrence, except under conditions of most extraordinary 

 external violence, as instantaneous death of all parts of the organism. If we confine 

 ourselves to physiological facts, we cannot admit the existence of a single vital principle 

 which animates the entire organism. Each tissue appears to have its peculiar property, 

 dependent upon its exact physiological constitution, which we call vitality ; a term 

 which really explains nothing. The tissues usually die successively, and not simulta- 

 neously, nearly all of them being dependent upon the circulating, oxygen-carrying blood 

 for the maintenance of their physiological properties. It has been demonstrated, in- 

 deed, that the so-called vital properties of tissues may be restored, after apparent death, 

 by the injection of blood into their vessels. 



After death, there is often a discharge of the contents of the rectum and bladder, 

 and parturition, even, has been known to take place. The appearance which indicates 

 growth of the beard after death is probably due to shrinking of the skin and, perhaps, 

 contraction of the smooth muscular fibres attached to the hair-follicles. The most 

 important phenomenon, however, which is observed before 'putrefaction begins, is a gen- 

 eral rigidity of the muscular system. 



Cadaveric Rigidity. At a variable period after death, ranging usually from five to 

 seven hours, all of the muscles of the body, involuntary as well as voluntary, become 

 rigid and can only be stretched by the application of considerable force. Sometimes, 

 especially after long-continued and exhausting diseases, this rigidity appears as soon as a 

 quarter of an hour after death. In the case of persons killed suddenly, while in full health, 

 it may not be developed until twenty or thirty hours after death, and it then continues 

 for six or seven days. Its average duration is from twenty -four to thirty-six hours ; 

 and, as a rule, it is more marked and lasts longer, the later it appears. In warm weather, 

 cadaveric rigidity appears early and continues for a short time. When the contraction 

 is overcome by force, after the rigidity has been completely established and has continued 

 for some time, it does not reappear. The rigidity of the muscular system extends to the 

 muscular coats of the arteries and the lymphatics. It is for this reason that the arterial 

 system is usually found empty after death. The rigidity first appears in the muscles 

 which move the lower jaw; then it is noted in the muscles of the trunk and neck, ex- 



