Boiling Frog - Scientific Background

Scientific Background

Several experiments involving recording the reaction of frogs to slowly heated water took place in the 19th century. In 1869, while doing experiments searching for the location of the soul, German physiologist Friedrich Goltz demonstrated that a frog that has had its brain removed will remain in slowly heated water, but his intact frogs attempted to escape the water.

Other experiments showed that frogs did not attempt to escape gradually heated water. An 1872 experiment by Heinzmann demonstrated that a normal frog would not attempt to escape if the water was heated slowly enough, which was corroborated in 1875 by Fratscher.

Goltz raised the temperature of the water from 17.5° C to 56° C in about ten minutes, or 3.8° C per minute, in his experiment which prompted normal frogs to attempt to escape, whereas Heinzmann heated the frogs over the course of 90 minutes from about 21 °C to 37.5 °C, a rate of less than 0.2 °C per minute. One source from 1897 says, "in one experiment the temperature was raised at a rate of 0.002°C per second, and the frog was found dead at the end of 2½ hours without having moved."

In 1888 William Thompson Sedgwick explained the apparent contradiction between the results of these experiments as a consequence of different heating rates used in the experiments: "The truth appears to be that if the heating be sufficiently gradual, no reflex movements will be produced even in the normal frog ; if it be more rapid, yet take place at such a rate as to be fairly called 'gradual', it will not secure the repose of the normal frog under any circumstances".

Modern sources tend to dispute that the phenomenon is real. In 1995, Professor Douglas Melton, of the Harvard University Biology department, said, "If you put a frog in boiling water, it won't jump out. It will die. If you put it in cold water, it will jump before it gets hot—they don't sit still for you." Dr. George R. Zug, curator of reptiles and amphibians at the National Museum of Natural History, also rejected the suggestion, saying that "If a frog had a means of getting out, it certainly would get out."

In 2002 Dr. Victor H. Hutchison, Professor Emeritus of Zoology at the University of Oklahoma, with a research interest in thermal relations of amphibians, said that "The legend is entirely incorrect!". He described how the critical thermal maximum for many frog species has been determined by contemporary research experiments: as the water is heated by about 2 °F, or 1.1 °C, per minute, the frog becomes increasingly active as it tries to escape, and eventually jumps out if the container allows it.