RESPIRATION: THE MECHANISM OF BREATHING 367 



Asphyxia. Asphyxia is death from suffocation, or want of 

 oxygen by the tissues. It may be brought about in various ways; 

 as by strangulation, which prevents the entry of air into the lungs; 

 or by exposure in an atmosphere containing no oxygen; or by 

 putting an animal in a vacuum ; or by making it breathe air con- 

 taining a gas which has a stronger affinity for hemoglobin than 

 oxygen has, and which, therefore, turns the oxygen out of the red 

 corpuscles and takes its place. The gases which do the latter are 

 very interesting since they serve to prove conclusively that the 

 Body can only live by the oxygen carried around by the hemo- 

 globin of the red corpuscles; the amount dissolved in the blood- 

 plasma being insufficient for its needs. Of such gases carbon 

 monoxid is the most important and best studied ; in the frequent 

 mode of committing suicide by stopping up all the ventilation 

 holes of a room and turning on the gas, it is poisoning by carbon 

 monoxid which causes death. 



The Phenomena of Asphyxia. As soon as the oxygen in the 

 blood falls below the normal amount the breathing becomes 

 hurried and deeper, and the extraordinary muscles of respiration 

 are called into activity. The dyspnoea becomes more and more 

 marked, and this is especially the case with the expirations which, 

 almost or quite passively performed in natural breathing, become 

 violently muscular. At last nearly all the muscles in the Body are 

 set at work ; the rhythmic character of the respiratory acts is lost, 

 and general convulsions occur, but, on the whole, the contractions 

 of the expiratory muscles are more violent than those of the in- 

 spiratory. 



The violent excitation of the nerve-centers soon exhausts them, 

 and all the more readily since their oxygen supply (which they like 

 all other tissues need in order to continue their activity) is cut off. 

 The convulsions therefore gradually cease, and the animal be- 

 comes calm again, save for an occasional act of breathing: these 

 final movements are inspirations and, becoming less and less fre- 

 quent, at last cease, and the animal appears dead. Its heart, how- 

 ever, though gorged with extremely dark venous blood still makes 

 some slow feeble pulsations. So long as it beats artificial respira- 

 tion can restore the animal, but once the heart has finally stopped 

 restoration is impossible. There are thus three distinguishable 

 stages in death from asphyxia. (1) The stage of dyspnoea. (2) 



