ABSTRACT
Freshwater turtles (Chrysemys picta bellii Gray) were acclimated to temperatures of 5, 10, 20 and 30°C for at least 12 days, and pulmonary ventilation, oxygen uptake and arterial pH, 
and 
were determined in completely unrestrained specimens. Oxygen uptake 
increased overproportionately (6·7-fold) as compared to pulmonary ventilation (
, 4·4-fold) when the temperature increased from 10 to 30°C. The observed rise in arterial 
from 13 (5 °C) to 32 mmHg (30°C) was the result of a decrease in 
, whereas an increase of arterial 
from 12Torr at 5°C to about 60Torr at 20 and 30°C mainly resulted from the effects of intracardiac blood shunting combined with temperature-dependent shifts of the oxygen dissociation curve. Arterial pH fell with rising temperature significantly less (ΔpH/Δt = −0·010U/°C) than required for constant relative alkalinity and for constant dissociation of imidazole. The changes of cerebrospinal fluid pH with temperature, calculated from the mean arterial 
values, were even smaller [ΔpH/Δtcsf = −0·008). It is concluded that the observed temperature dependence of the acid-base status is not in agreement with the alphastat hypothesis.
