210 HAND-BOOK OF PHYSIOLOGY. 



and, more or less, of all the muscles of the body; lividity of the skin and 

 all other vascular parts, while the veins are also distended, and the tissues 

 seem generally gorged with blood; convulsions, quickly followed by in- 

 sensibility, and death. 



The conditions which accompany these symptoms are 



(1) More or less interference with the passage of the blood through 

 the pulmonary blood-vessels. 



(2) Accumulation of blood in the right side of the heart and in the 

 systemic veins. 



(3) Circulation of impure (non-aerated) blood in all parts of the body. 

 Cause of Death from Asphyxia. The causes of these conditions 



and the manner in which they act, so as to be incompatible with life, may 

 be here briefly considered. 



(1) The obstruction to the passage of blood through the lungs is not 

 so great as it was once supposed to be; and such as there is occurs chiefly 

 in the later stages of asphyxia, when, by the violent and convulsive action 

 of the expiratory muscles, pressure is indirectly made on the lungs, and 

 the circulation through them is proportionately interfered with. 



(2) Accumulation of blood, with consequent distension of the right 

 side of the heart and systemic veins, is the direct result, at least in part, 

 of the obstruction to the pulmonary circulation just referred to. Other 

 causes, however, are in operation, (a) The vaso-motor centres stimu- 

 lated by blood deficient in oxygen, causes contraction of all the small 

 arteries with increase of arterial tension, and as an immediate conse- 

 quence the filling of the systemic veins, (b) The increased arterial ten- 

 sion is followed by inhibition of the action of the heart, and, thus, the 

 latter, contracting less frequently, and gradually enfeebled also by defi- 

 cient supply of oxygen, becomes over-distended by blood which it cannot 

 expel. At this stage the left as well as the right cavities are distended 

 with blood. 



The ill effects of these conditions are to be looked for partly in the heart, 

 the muscular fibres of which, like those of the urinary bladder or any 

 other hollow muscular organ, may be paralyzed by over-stretching; and 

 partly in the venous congestion, and consequent interference with the 

 function of the higher nerve-centres, especially the medulla oblongata. 



(3) The passage of non-aerated blood through the lungs and its dis- 

 tribution over the body are events incompatible with life, in one of the 

 higher animals, for more than a few minutes; the rapidity with which 

 death ensues in asphyxia being due, more particularly, to the effect of 

 non-oxygenized blood on the medulla oblongata, and, through the coro- 

 nary arteries, on the muscular substance of the heart. The excitability 



.of both nervous and muscular tissue is dependent on a constant and large 

 supply of oxygen, and, when this is interfered with, is rapidly lost. The 

 diminution of oxygen, it may be here remarked, has a more direct in- 



