578 PHILOSOPHICAL TRANSACTIONS. [anNO 17 6U 



hunger and inspiration, and, by its bearing firmly against the sides of the auricles, 

 to support and strengthen them against too great distentions : for the cavitv of 

 the pericardium seems to be but little more than commensurate to the bulk of its 

 contents, when one half of them are filled and the other half empty. This will 

 appear on endeavouring to fill the heart, with its auricles, and its 2 great arteries, 

 with wax, at the same time while it is inclosed in the pericardium ; in which ex- 

 periment, one or other of these cavities will be found to have been so compressed 

 by the pericardium, as to have refused a free admittance to the wax, and will 

 therefore be found proportionably empty. 



The elastic texture, connexions, and capacity of the pericardium, being thus 

 stated, let us now consider the order in which the several distentions must have 

 arisen in the two great arteies and cavities of the heart, with the necessary 

 effects of those distentions on the pericardium and the parts which it contains. 



The first distention (and this a great and violent one) must have arisen in the 

 aorta ; and the consequent pressure on the pulmonary artery, by the aorta so 

 distended, must have been sufficient (either by degrees or at once) to stop the 

 blood's discharge out of the right ventricle and pulmonary' artery, and to distend 

 both those cavities beyond their natural state of repletion. So that under these 

 circumstances the 2 great arteries and the right ventricle, must have been under 

 an extraordinary and continual distention, and consequently an increase of bulk 

 at the same time ; whereas, in the natural state of the body, these 3 cavities are 

 alternately dilated and contracted, and the right ventricle is always proportionally 

 diminished in bulk, as the pulmonary artery is increased, and vice versa. So 

 that with respect to these three great cavities, (supposing that their several dis- 

 tentions had been no greater than natural) the pericardium must have been 

 obliged to contain one third more in proportion than its capacity was formed to 

 receive. During this time, the blood being stopped in its passage through the 

 lungs, and its afflux to the left auricle and ventricle being thereby suspended, the 

 left auricle and ventricle must have remained in a contracted state ; in conse- 

 quence of which the right ventricle had ample space in the pericardium, to admit 

 that degree of distention, which was previously requisite for its bursting. But 

 the right auricle (being fixed to its station by its connections with the left 

 auricle and the pericardium, and being firmly compressed against the pericardium, 

 by the aorta, the pulmonary artery, and the right ventricle, all which appear to 

 have been, at this time, greatly distended beyond their natural bulk) must have 

 been thereby deprived of the space in the pericardium necessary to admit of its 

 being distended ; and the whole surcharge and distention must, by the pressure 

 of the pericardium on the auricle, necessarily have been confined to the right 

 ▼entricle till it burst. 



Had these surcharges arisen in any other order, their effects must have been 



