SOME FACTORS GOVERNING THE INITIATION OF RESPIRATION IN THE CHICK

Abstract

The chick fetus begins to breath air about 24 hrs. before it hatches on the 21st day. Rhythmic respiratory movements made their appearance normally at about 18 days of incubation. Rhythmic respiratory movements were initiated 4-6 days prematurely by administration of 1.6% CO2. A state of O deficiency brought about slowly by administering nitrogen was less certain to stimulate such movements. Anoxemia produced suddenly always did so after a latent period as early as the middle of incubation. The respiratory rhythm which appeared in low O atmospheres seemed to be associated with impairment of heart action. Both CO2 and anoxemia at first led to an increase of all somatic movements. This period of activity was quickly followed by depression of the finer wing and foot movements leaving only those activities involved in respiration. The appearance of deep rhythmic respiratory movements seemed to be accompanied by an increase in tonus of the muscles involved in these movements.