Fig. 4. Capacitance curves. Mean circulatory filling pressure (MCFP) as a function of a change in blood volume (ml kg^-1) in anaesthetised South American rattlesnakes Crotalus durissus. 0 ml kg^-1 represents normal blood volume and the control value. Values in parentheses represent blood volume, assuming this species to have a blood volume of 54 ml kg^-1. Black symbols represent the untreated snakes and grey symbols represent the -blocked snakes. Triangles indicate control values at normal blood volume. A weighted linear regression curve has been fitted to each group of snakes, where the black curve (y=0.306x+10.17) and the grey curve (y=0.256x+9.14) represent the untreated and the -blocked animals, respectively. Arrows indicate unstressed blood volumes. Values are means ± S.E.M.(N=6). Asterisks indicate a significant difference relative to control values. (1 cm H₂O=0.098 kPa.)