850 SPECIAL PHYSIOLOGY. 



convulsions, coma, and death. Sometimes vomiting occurs, and occa- 

 sionally death ensues from apoplexy. On examination, after death, 

 the cerebral vessels are found congested, and serous exudations to be 

 present in the ventricles and at the base of the brain ; sometimes clots 

 of blood are found in the substance of the brain. Carbonic acid is the 

 choke-damp of mines. 



Asphyxia. 



When a person is completely immersed in an atmosphere of almost 

 pure carbonic acid, as in brewers' vats, in cellars in which wine is fer- 

 mented, or in caverns, such as the Grotto del Cane, death occurs much 

 more rapidly; the glottis is sometimes spasmodically closed, and res- 

 piration is as completely arrested by this impediment to the passage 

 of air, as it is in strangulation, or in any other mechanical form of 

 suffocation. Even if the glottis should remain patent, the entire ab- 

 sence of oxygen from such an atmosphere, would produce suffocation 

 almost as speedily; for twenty seconds is the extreme time during 

 which the breath can' be held by voluntary effort; so that suffocation 

 might be said to commence at the expiration of that brief period. In 

 any case, the form of death, which so rapidly ensues, is that by 

 asphyxia, the essential characters of which are, loss of muscular power 

 and consciousness, cessation of the movements of the chest, and then 

 of the pulsations of the heart, with accumulation of blood in the right 

 side of that organ, and in the whole venous system, so that even the 

 skin becomes livid. The blood remains a long time fluid. 



The mode in which death occurs from asphyxia, whether caused by 

 compression of the chest and abdomen, by direct suffocation from ex- 

 ternal strangulation, internal choking, or spasmodic closure of the 

 glottis, or whether produced indirectly by immersion in some irrespi- 

 rable gas, or in water, by paralysis of the respiratory nervous centres, 

 or by narcotic poisonings, is somewhat complicated. The respiratory 

 interchanges of carbonic acid and oxygen, between the blood in the 

 pulmonary capillaries and the air in the air-cells, diminish or cease ; 

 the venous blood, reaching the lungs, no longer gives off its carbonic 

 acid, and the pulmonary capillary circulation is more or less quickly 

 stopped. The forward effects of this are, that the left side of the 

 heart receives, at first, imperfectly aerated blood, and then little or no 

 blood at all, so that the functions of the brain and nervous centres, of 

 the muscular system, and of the heart itself, all of which require, for 

 their maintenance, a due supply of arterial blood, gradually or rapidly 

 cease ; ultimately, the left side of the heart and the arteries, accom- 

 modating themselves by their muscular contractility and elasticity, are 

 nearly or entirely emptied, or contain but very small quantities of dark 

 non-aerated blood. On the other hand, the backward effects of the 

 arrested circulation in the pulmonary capillaries, are ultimately to 

 distend the right side of the heart, and the entire venous system, with 

 very dark blood. The stagnation of the blood in the pulmonary capil- 

 laries, which is the first stage of the fatal process, has been attributed 

 to some direct influence of the carbonic acid on the blood corpuscles ; 



