CHAPTER III.

OF THE INFLUENCE OF THE DEATH OF THE HEART OVER THAT OF THE LUNGS.

The lungs are the seat of two very different sorts of phenomena. The first, which are entirely mechanical, are relative to the rise and fall of the ribs and diaphragm, to the dilatation and contraction of the air vessels, and to the entry and exit of the air, which is the effect of these movements. The second, which are purely chemical, may be referred to the different alterations, which the air and blood experience.

These two sorts of phenomena have a mutual dependence on each other. Without the mechanical, the chemical changes could not be made; without the chemical changes, the blood would cease to become an excitant to the brain, in consequence of which that organ would no longer operate upon the diaphragm or intercostal muscles; the muscles themselves would then become inactive, and the motions of the thorax be annihilated. These phenomena, however, are put an end to in a different manner by the death of the heart, accordingly as it happens on one or the other side.

I. _In what manner are the actions of the lungs interrupted, when the black-blooded heart ceases to act?_

The heart has certainly no influence over the mechanical functions of the lungs, but it contributes essentially to produce the chemical changes which are made there, by sending thither the fluid which is destined to undergo a change. When its functions then are interrupted as may happen from wounds or be occasioned by ligature, the chemical changes which should be made in the blood, are suddenly suppressed; though the air continue to enter into the lungs, from the dilatation and contraction of the chest.

Meanwhile there arrives nothing at the red-blooded heart, or[68] so little as to be insufficient for the production of the cerebral movements. The functions of the brain are consequently suspended, and of course the movements of the diaphragm and ribs.

II. _In what manner are the actions of the lungs interrupted, when those of the red-blooded heart are suspended?_

Whenever from wound, ligature, or aneurism, the functions of the red-blooded heart or aorta cease, the functions of the lungs are terminated in the following order:

1st. There is no further impulse made upon the brain. 2dly, No further movement of that organ.[69] 3dly, No further action exercised upon the muscles. 4thly, No further contraction of the intercostals or diaphragm. 5thly, The mechanical functions of the lungs cease. 6thly, Their chemical functions cease.

In the former case, the chemical changes could not be made for want of blood. Here they cannot be made for want of air. Such is the difference in the death of the lungs, in consequence of that of the heart, according as the latter is affected. But as the circulation is very rapid, there cannot be but a very short interval between the interruption of the chemical and the mechanical functions of the lungs.

FOOTNOTES:

[68] After the obliteration of the ductus arteriosus, the left ventricle receives no blood but what comes from the lungs; now, if the motions of the thorax continue, it is red blood; at least so long as the air is freely admitted into the bronchial tubes, and so long as the composition of this fluid is not changed by the mixture of foreign gases.

[69] These two modifications should, after what we have said, be reduced to a single one, viz. want of excitement of the brain by the arterial blood.