On the Resistance to Asphyxia of the Duck in Diving

In the duck, the relation between the rate of the heart and that of respiration is very close. With inspiration, as in mammals, there is quickening of the heart‐rate; with expiration, slowing, which becomes marked if this phase be prolonged. Thus slowing or stoppage of breathing, however produced, causes a corresponding slowing of the heart—the length of the pause, not the agency which produces it, being the important factor. Thus submersion of the duck's head gives rise to slowing of the heart, because it produces apnœa; occlusion of the trachea, on the other hand, causes but little change in respiration, and under its influence slowing of the heart is less marked. Slowing of the heart and the fact of apnœa aid the duck in resisting asphyxia from submersion, because oxygen is spared by the decreased metabolism of the heart and respiratory muscles, and by the absence of mechanical circulation of the air in the respiratory tract. One reason why, in the duck, asphyxia in air is more rapid than in water must be that in this case there is little sparing of oxygen in this way.