|
Main
- books.jibble.org
My Books
- IRC Hacks
Misc. Articles
- Meaning of Jibble
- M4 Su Doku
- Computer Scrapbooking
- Setting up Java
- Bootable Java
- Cookies in Java
- Dynamic Graphs
- Social Shakespeare
External Links
- Paul Mutton
- Jibble Photo Gallery
- Jibble Forums
- Google Landmarks
- Jibble Shop
- Free Books
- Intershot Ltd
|
books.jibble.org
Previous Page
| Next Page
Page 15
Old age in itself is seldom a cause of death. In rare cases in the
very old a condition is found in which no change is present to which
death can be attributed, all organs seem to share alike in the
senescence. Death is usually due to some of the accidents of life, a
slight infection to which the less resistant body succumbs, or to the
rupture of a weakened blood vessel in the brain, or to more advanced
decay in some organ whose function is indispensable. The causes and
conditions of age have been a fertile source for speculation. Many of
the hypotheses have been interesting, that of Metschnikoff, for
example, who finds as a dominating influence in causing senescence the
absorption of toxic substances formed in the large intestine by
certain bacteria. He further finds that the cells of the body which
have phagocytic powers turn their activity against cells and tissues
which have become weakened. There may be absorption of injurious
substances from the intestines which the body in a vigorous condition
is able to destroy or to counteract their influence, and these may be
more operative in the weaker condition of the body in the old.
Phagocytes will remove cells which are dead and often cells which are
superfluous in a part, but there is no evidence that this is ever
other than a conservative process. Since it is impossible to single
out any one condition to which old age is due, the hypothesis of
Metschnikoff should have no more regard given it than the many other
hypotheses which have been presented.
Death of the body as a whole takes place from the cessation of the
action of the central nervous system or of the respiratory system or
of the circulation. There are other organs of the body, such as the
intestine, kidney, liver, whose function is essential for life, but
death does not take place immediately on the cessation of their
function. The functions of the heart, the brain and the lungs are
intimately associated. Oxygen is indispensable for the life of the
tissues, and its supply is dependent upon the integrity of the three
organs mentioned, which have been called the tripos of life.
Respiration is brought about by the stimulation of certain nerve cells
in the brain, the most effective stimulus to these cells being a
diminution of oxygen in the blood supplying them. These cells send out
impulses to the muscles concerned in inspiration, the chest expands,
and air is taken into the lungs. Respiration is then a more
complicated process than is the action of the heart, for its
contraction, which causes the blood to circulate, is not immediately
dependent upon extrinsic influences. Death is usually more immediately
due to failure of respiration than to failure of circulation, for the
heart often continues beating for a time after respiration has ceased.
Thus, in cases of drowning and suffocation, by means of artificial
respiration in which air is passively taken into and expelled from the
lungs, giving oxygen to the blood, the heart may continue to beat and
the circulation continue for hours after all evident signs of life and
all sensation has ceased.
By this general death is meant the death of the organism as a whole,
but all parts of the body do not die at the same time. The muscles and
nerves may react, the heart may be kept beating, and organs of the
body when removed and supplied with blood will continue to function.
Certain tissues die early, and the first to succumb to the lack of
oxygenated blood are the nerve cells of the brain. If respiration and
circulation have ceased for as short a time as twelve minutes, life
ceases in certain of these cells and cannot be restored. This is again
an example of the greater vulnerability of the more highly
differentiated structure in which all other forms of cell activity are
subordinated to function. There are, however, pretty well
authenticated cases of resuscitation after immersion in water for a
longer period than twelve minutes, but these cases have not been
carefully timed, and time under such conditions may seem longer than
it actually is; and there is, moreover, the possibility of a slight
gaseous interchange between the blood and the water in the lungs, as
in the case of the fish which uses the water for an oxygen supply as
the mammal does the air. There are also examples of apparent death or
trances which have lasted longer, and the cases of fakirs who have
been buried for prolonged periods and again restored to life. In these
conditions, however, all the activities of the body are reduced to the
utmost, and respiration and circulation, so feeble as to be
imperceptible to ordinary observation, suffice to keep the cells
living.
With the cessation of life the body is subject to the unmodified
action of its physical environment. There is no further production of
heat and the body takes the temperature of the surroundings. The only
exceptions are rare cases in which such active chemical changes take
place in the dead body that heat is generated by chemical action. At a
varying interval after death, usually within twelve hours, there is a
general contraction and hardening of the muscles due to chemical
changes, probably of the nature of coagulation, in them. This begins
in the muscles of the head, extends to the extremities, and usually
disappears in twenty-four hours. It is always most intense and most
rapid in its onset when death is preceded by active muscular exertion.
There have been cases of instantaneous death in battle where the body
has remained in the position it held at the moment of death, this
being due to the instantaneous onset of muscular rigidity. The blood
remains fluid for a time after death and settles in the more dependent
parts of the body, producing bluish red mottled discolorations. Later
the blood coagulates in the vessels. The body loses moisture by
evaporation. Drying of the surface takes place where the epidermis is
thin, as over the transparent part of the eye and over areas deprived
of epidermis. Decomposition and putrefaction of the body due to
bacterial action takes place. The bacteria ever present in the
alimentary canal make their way from this into the dead tissue.
Certain of these bacteria produce gas which accumulates in the tissues
and the body often swells enormously. A greenish discoloration
appears, which is due to the union of the products of decomposition
with the iron in the blood; this is more prominent over the abdomen
and appears in lines along the course of the veins. The rapidity with
which decomposition takes place varies, and is dependent upon many
factors, such as the surrounding temperature, the nutrition of the
body at the time of death, the cause of death. It is usually not
difficult to recognize that a body is dead. In certain cases, however,
the heart's action may be so feeble that no pulse is felt at the
wrist, and the current of the expired air may not move a feather held
to the nostril or cloud the surface of a mirror by the precipitation
of moisture upon it. This condition, combined with unconsciousness and
paralysis of all the voluntary muscles, may very closely simulate
death. The only absolute evidence of death is given by such changes as
loss of body heat, rigor mortis or stiffening of the muscles,
coagulation of the blood and decomposition.
Previous Page
| Next Page
|
|