We see by this and the preceding experiments, that we cannot adopt without modification the expression of Haller and Lorry relative to the swelling of the veins. This swelling takes place, not only, as they say, by the flowing back of the blood of the venæ cavæ into the branches which open into them mediately or immediately, but also by the entrance into the vein of a greater quantity of blood coming from the arteries. [80] As in dead bodies the air within and the air without are of the same temperature, the lungs, when they are full of it, do not flatten when the thoracic cavity is opened. There is usually then a space between the parietes and the contained organs; this is not because we die in expiration; for as the lungs empty themselves, the ribs and intercostal muscles rest upon them; it is because the pulmonary air, in cooling occupies less space, and the cells contracting gradually as the cooling takes place, diminish the whole size of the organ. A vacuum is then made between the pectoral and pulmonary portions of the pleura. It is thus that, under some circumstances, the brain flattening and lessening after death, whilst the cavity of the cranium remains the same, a vacuum is formed between these two parts, which then exhibit an arrangement different from that of the living organs. If the sacs without an opening, as the peritoneum, tunica vaginalis, &c. never resemble, in this respect, the pleura and arachnoides; if their different surfaces are always contiguous after death, it is because the abdominal parietes or the skin of the scrotum, unable to resist the external air, flatten by pressure, and are brought against the internal organs, as the diminution of these tends to form a vacuum. It is to this vacuum existing in the pleura of dead bodies, that must be referred the following phenomenon, which is always observed when the abdomen is opened and the diaphragm dissected. In fact, as long as no opening is made in this muscle, it remains distended and concave, notwithstanding the weight of pectoral viscera which rest upon it in a perpendicular situation, because the external air, which presses the concavity of it, forces it then into the vacuum in the thorax, which never exists during life. But the instant the air is admitted by a cut of the scalpel, this muscular partition flattens, because the equilibrium is established. If all the air is drawn from the lungs by a syringe, the diaphragmatic arch is still more evident. There is then this difference between the opening of a dead body and that of a living one, that in the first the lungs are already flattened, and in the second they flatten at the instant of opening. The contraction of the cells, from the condensation of the air by cooling, is an effect of the contractility of texture or from want of extension, which as we have said, continues in a degree with the organs after death.