On the Regulation of the Respiration in Reptiles

Abstract

1. In two species of Lacerta (L. viridis and L. sicula) the effects on respiration of body temperature (changes in metabolic rate) and of CO₂ added to the inspired air were studied. 2. Pulmonary ventilation increases when body temperature increases. The increase is brought about by an increase in respiratory frequency. No relationship is found between respiratory depth and temperature. 3. The rise in ventilation is provoked by the needs of metabolism and is not established for temperature regulating purposes (in the temperature interval 10°-35°C). 4. The ventilation per litre O₂ consumed has a high numerical value (about 75, compared to about 20 in man). It varies with the body temperature and demonstrates that the inspired air is better utilized at the higher temperatures. 5. Pulmonary ventilation increases with increasing CO₂ percentages in the inspired air between o and 3%. At further increases in the CO₂ percentage (3-13.5%) it decreases again. 6. At each CO₂ percentage the pulmonary ventilation reaches a steady state after some time (10-60 min.) and is then unchanged over prolonged periods (1 hr.). 7. The respiratory frequency in the steady state decreases with increasing CO₂ percentages. The respiratory depth in the steady state increases with increasing CO₂ percentages. This effect of CO₂ breathing is not influenced by a change in body temperature from 20° to 30°C. 8. Respiration is periodically inhibited by CO₂ percentages above 4%. This inhibition, causing a Cheyne-Stokes-like respiration, ceases after a certain time, proportional to the CO₂ percentage (1 hr. at 8-13% CO₂), and respiration becomes regular (steady state). Shift to room air breathing causes an instantaneous increase in frequency to well above the normal value followed by a gradual decrease to normal values. 9. The nature of the CO₂ effect on respiratory frequency and respiratory depth is discussed, considering both chemoreceptor and humoral mechanisms.