The direct cause of death and how it is that when a certain portion of the mechanism of the system is deranged, the whole machine may cease its motion, is an interesting subject of inquiry.

In looking at the human system, we notice what ample provisions have been made for maintening life. We have, first, the heart and the blood-vessels, which connect with and are distributed to every part of the system. Next we have the lungs, and the case in which they are lodged. And lastly, the power which works and regulates the machine vested in the nervous system. The main organs of these systems, the heart, the lungs, the brain, are called vital organs, and if the functions of one are arrested, the other two speedily cease.

That the heart may force the blood from its chambers, a certain power of contraction is necessary, and also, the presence of a sufficient quantity of blood in the chambers of the heart to stimulate them to contract. If this stimulus is withheld, or is diffident, the heart will soon cease to beat.

Respiration is subservient to the circulation of the blood. The heart and the lungs respond to each other, the blood being sent from the right heart to the lungs to be arterialized, when it is conveyed back to the heart, and is then distributed to every part of the system.

But to carry on respiration two things are necessary; first, air to enter the lungs and depart at intervals, and second, the movements of the chest, to cause its entrance and exit. These movements, although they may be regulated by the will, are essentially involuntary. The act of respiration depends on a certain condition of the medulla oblongata, and if this condition fails, there is no action of the chest, no expansion of the lungs, no inhalation of air. and consequently no chemical change in the blood. Respiration therefore is dependent directly on the nervous system, and the cases are by no means rare where the nervous system receives a heavy shock, that the chest is paralyzed, and the lungs rendered incapable of performing their duty, thus causing death.

In death by aenemia the supply of blood for the heart fails. The heart retains the power of contraction, but there is no blood to contract upon. We see a striking instance of this in sudden and profuse haemorrhage. The countenance and lips become exceedingly pale, cold sweats cover the 'body, the pupils are dilated, the sight becomes dim, the pulse is weak and faint, and insensibility speedily follows. In connection with these symptoms there is often nausea, vomiting, excessive restlessness, and tossing of the limbs, delirium, and convulsions; breathing faint and gasping, and this struggling for breath so violent that the cold sweat stands in drops upon the forehead, gradually grows fainter and fainter until death closes the scene. We see a train of symptoms similar to the above in the soldier bleeding to death on the battle-field, in the mother flooding after child-birth, and in those cases where large blood-vessels are wounded. In death by aenemia the cessation of the nervous functions is occasioned by the lack of blood which should pass to the brain. The effect of position illustrates this. Syncope will much more rapidly ensue on venesection, where the patient is in an upright posture than when he is reclining. Hence in case of syncope we place the head as low if not lower than the trunk of body, so that the blood may more readily pass to the brain.

Death by asthenia is directly the converse of the above. Here the nervous system is the part first affect-ed, and through it the heart or lungs. The heart may be full of blood, yet its power of contraction is gone. Death by asthenia is sometimes produced by causes which act primarily through the nervous system, such as intense grief, joy, and terror. Death occurring from blows on the epigastrium, from concussion where the brain is jarred, and from electricity - are of this kind. The phenomena are different, when death by asthenia occurs more slowly, from disease, especially in malignant cholera, mortification, and acute inflammation of the peritoneum. In these cases the muscular debility is extreme, but the intellect is clear, and the hearing sometimes painfully acute. In lingering disorders where there is a long-continued drain on the system, the cause of death is owing in part to both anemia and asthenia. Death from want of a proper arterialization of the blood may be caused by some impediment which prevents the introduction of air into the lungs, or by insensibility of the muscles required for breathing, caused by disease or injury of the brain and nervous system. In the latter case it is generally denominated coma, in the former it is termed asphyxia. The means by which air, or oxygen, which is its vital principle, is prevented from entering the lungs are various. Azotic, hydrogen, or carbonic acid gases, all incapable of maintaining life, may be prevented by submersion, and to death from this cause we give the name of drowning; or by stoppage of the mouth and nostrils - smothering; by mechanical obstruction of the. larynx and trachea from within, as by food - choking; or from without, as with a cord - strangulation; or by impeding the mechanical action necessary for the admission and expulsion of air. The mechanism of respiration consists in an elevation and depression of the ribs, performed partly by the action of the intercostal muscles, and partly by the descent and ascent of the diaphragm and the action of the abdominal muscles. If motion both of the diaphragm and ribs be at the same time stopped, the result is death by as-phy.cia. This happens with persons who in digging are buried, with the exception of their head, by a mass of earth. A cast was attempted to be taken in one entire piece, as an academic model, of the body of an athletic black man. As soon as the plaster began to set, he felt on a sudden, deprived of the power of respiration, and to add to his misfortune was cut off from the means of expressing his distress; his situation was perceived just in time to save his life. The same immoveable state of the lung-case is sometimes produced in tetanus, or poisoning by strychnine, or from disease or injury of the spinal chord above the origin of the nerves that give off the phrenic nerve; by section of the phrenic and intercostal nerves, and by ruptures in the walls of the thorax, through which air is admitted to the lungs, also when the pleura become filled with liquid of any kind.