From the moment it reaches the thoracic cavity the foreign object makes its way towards the channel formed on either side by the ribs and below by the sternum, and therefore towards the point of the heart. This is the second phase of development.
The passage of the foreign body through the diaphragm occupies a more or less considerable time, depending on its length; the beginning of this second phase is characterised by relative immobility of the circle of the hypochondrium during respiration. The abnormal sensibility and pain impede contraction of the diaphragm.
Palpation of the region of the xiphoid cartilage then reveals abnormal sensibility, and sometimes causes the animal to resent being handled.
From this time the pericardial symptoms proper commence, the foreign body having come in contact with the pericardium. This phase, unlike those which precede it, presents well-defined symptoms. The irritation of the heart and its ganglionic system by a foreign body in the pericardium is shown by considerable acceleration of the heart beats even before there is any exudation into the pericardial sac. Instead of 60 to 70 beats, the normal number, the pulse may rise to 80, 90, 100, or even 110 beats per minute. The heart sounds are tumultuous, dull and ill-defined, while the pulse appears bounding and strong.
But this period of cardiac excitement while persisting is soon complicated by other symptoms. As soon as the foreign body penetrates the pericardial sac, there is infection, which produces an active form of inflammation and abundant exudation. From this time the pulse becomes weaker and weaker, until, under the steadily increasing pressure on the heart, it is almost imperceptible.
There is only moderate fever. As soon as the exudation becomes considerable, the symptoms of pericarditis grow very marked: they may be grouped in the following order, according to their importance.
A. Cardiac symptoms. On palpation of the cardiac zone on the left the impulse of the heart is no longer felt. Percussion, which under normal circumstances reveals only partial dulness, now seems to give pain, and indicates abnormal dulness distributed in a vertical plane. The pulmonary lobes between the pericardium and thoracic walls are thrust upwards. The distended pericardial sac approaches the parietal layer of the pleura and may adhere to it, hence the dulness. This dulness extends as far back as the xiphoid appendix of the sternum, and can be detected on both sides, marginated above by a convex line.
In rare cases the dulness is absent, being partially replaced by tympanitic resonance, due to the presence of gases in the distended pericardial cavity, which gases originate in the digestive reservoirs or result from putrid fermentation of the pericardial exudate.
Simple or double pleurisy, or even pneumonia of the cardiac lobes resulting from infection by contiguity, may complicate cases of rapid pericarditis. The dulness then appears modified, as do the signs observed on auscultation.
Auscultation furnishes valuable indications. From the outset it reveals acceleration of the heart. At a later stage, but only for a short time, it permits of the detection of the pericardial rubbing sound which precedes serous exudation, and which may persist for several days when large quantities of false membrane are produced.