From the frequency of deaths beginning with an embarrassment of the lungs, may be conceived also the reason, why this organ is so frequently gorged with blood in the carcase in general, the longer the agony, the heavier and fuller are the lungs. When such fulness is found, together with black blood in the red-blooded system, whatever the disease may have been, it may be pronounced that death has begun in the lungs. In fact the concatenation of the phenomena of death is from one of the three organs, from the lungs, brain, or heart, to all the others. Now when death begins in the heart, the pulmonary vessels are generally empty, and there is red blood in the aortic system. On the other hand, if death has begun in the brain, there is then indeed a certain quantity of blood in the arteries, but the lungs are empty, unless, when gorged with blood, by some antecedent affection.
[100] When the diaphragm is ruptured, a sudden cessation of the functions is not always the result of this accident. Patients have been known to survive many days, and the cause of death has only been ascertained by examining the body.
The intercostal muscles are, in this case, the sole agents of respiration, which becomes nearly analogous to that of birds or to that of animals with red and cold blood, who are destitute of the septum between the thorax and abdomen.[101]
Lieutaud cites various ruptures of the diaphragm, produced by other causes than external injuries. Diemerbroech has seen this muscle wanting in an infant who still lived to the age of seven years.
[101] When from any cause, the diaphragm cannot contract, the enlargement of the thorax is effected solely by the elevation of the ribs, and as this motion is then very evident, we can then appreciate better the influence the intercostal muscles have in its production in ordinary respiration. Haller, as is well known, supposed that the first rib was almost immoveable, and that the muscles in the first intercostal space, took it as their fixed point to elevate the second. This second rib, in its turn, served as a fixed point to elevate the third, and thus on to the last rib. But if we observe the mechanical phenomena of respiration when the diaphragm does not contract, as is the case in diaphragmatic pleurisy, we see that the first rib is far from being immoveable. Now, we cannot conceive how the intercostals which are attached to its inferior part, can, by contracting, assist in raising it. Besides, in order to elevate the ribs, a very great resistance must be overcome, and the intercostal muscles are too slender to induce us to suppose that they are capable of effecting it. The principal agents of this motion then are the anterior and posterior scaleni, which are distinctly seen to contract in great inspirations, the supra-costales and the muscles of the neck which attach it to the sternum. We ought to add to these a muscle, to which this use has never before been attributed; I mean the diaphragm. This muscle in fact in its contraction tends to become flat, from being concave as it is in inspiration. Now, its middle part in depressing the abdominal viscera experiences a certain resistance, and takes, as it were, from them a fixed point, by means of which it elevates the base of the thorax to which its circumference is attached.