I did a bit of research on the boiling frog phenomenon. It turned out that:

  1. In the 19th century, there have been done three experiments in which a frog in water was heated very slowly. It didn't jump out and then it died.
  2. Modern experiments did also heat frogs, and they did jump out.
  3. Actually, a frog dies in water of $40^{\circ}$ C. Therefore, to properly conduct the experiment the water should be heated from a normal temperature to 40 degrees.

In order to prove that the 19th century experiments were wrong, there should be a modern experiment where the frog is heated just as slowly as in the 19th century. According to Edward Wheeler Scripture (see Wikipedia), he performed the experiment with a rate of 0.002 degrees per second.

Are there modern experiments which also have such a slow rate? What is the slowest rate of a modern experiment?

EDIT The following article claims that the modern experiment with the slowest rate is still 9 times as fast as that of Scripture. Is this really true?

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    $\begingroup$ If the current climate science stats are accurate, all frogs on earth are being heated at a rate of 0.2° C per decade, on average. Sure, there may be a few covariates to account for, but the sample size is huge. $\endgroup$
    – acvill
    Mar 15, 2022 at 14:34
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    $\begingroup$ As noted in one of your links: "they don't sit still for you" seems to be the problem. If you put a frog in a pot, it doesn't matter if you heat it at all, if you allow them to escape they will escape. I kind of doubt anyone has actually published on that, though; people don't usually publish such trivialities. $\endgroup$
    – Bryan Krause
    Mar 15, 2022 at 15:39
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    $\begingroup$ @Riemann It seems the modern commentators are saying that the frog doesn't need any temperature increase to escape. If you put a frog in a pot it will jump out if it can, heat or no heat, so they don't see the point to do the experiment with a gradual temperature change. Presumably in the original experiment (which I haven't read) the frog was not actually able to escape, otherwise it would have (again, not because of heat, but because of frogs doing frog things, like moving around freely when they can). $\endgroup$
    – Bryan Krause
    Mar 15, 2022 at 16:34
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    $\begingroup$ OP: The most amazing of all your statements is that a dead frog jumped out of hot water! No wonder the experiment could not be reproduced! ("...a frog in water was heated very slowly. It didn't jump out until it died.") Like I said, that is one for the books. Or if one prefers journals, The Journal of Irreproducible Results. $\endgroup$ Mar 15, 2022 at 17:00
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    $\begingroup$ I don't really read enough German to read Heinzmann, but it seems that most, if not all, of his experiments were done in decerebrate frogs. It's a study of the reflex arc of the frog's leg and spine, rather than the behavior of the frog, from what I can tell. $\endgroup$
    – Bryan Krause
    Mar 15, 2022 at 17:18

1 Answer 1


To clear up some things, I have made a partial answer here.

While it is old, you shouldn't discount the observations made by scientists from the 1800's. Many great scientists from this period laid the foundations for science as we know it now. These include names such as Charles Darwin, Alfred Wallace, Robert Koch, Gregor Mendel, and Louis Pasteur, to name a few well known biologists, whom no-one would think to doubt. Scientists in the 1800s were certainly exact in their measurements, observations and records, and I don't doubt that the observations that they made were exactly what they claimed they were.

To this end, I had a look at Goltz's 1869 book1 (PDF here) in the original German, and put it through Google translate ('cause I don't read German well enough to follow at this level) at the relevant point. Fortunately the PDF linked is text-selectable, so I was able to copy this directly and edit some minor misinterpretations from the paste. Google translate is pretty good for German and German has not changed significantly since the 1800's I believe.

Here's the bits I copied from pages 127 and 128 (you can see the errors at line-ends and in special characters, and where some bits can't be recognized as they are in the spine end of the text):

Von drei gleichzeitig gefangenen, gleich grossen und reiz- :en Fröschen schneide ich zweien mit der glühenden Platin- linge des galvanokaustischen Apparats die Köpfe ab. Dem tten sonst unversehrten blende ich die Augen, um unnütze will- 1 liehe Bewegungen desselben möglichst auszuschliessen. Darauf ce ich den zuletzt geköpften Frosch in ein weites blechernes iäss, dessen Boden mit mehreren Schichten Leinwand bekleidet und bringe ihn sogleich in die hockende Stellung, welche hirnte Frösche immer annehmen und dann nicht wieder von ')St verlassen. Das Gefäss fülle ich jetzt so weit mit Wasser, 'S nur ein kleiner Theil des Thieres daraus hervorragt. Zu 1 Enthaupteten setze ich dann den geblendeten Frosch, wel- r sich alsbald ebenfalls in hockender Stellung niederlässt und iangslos verharrt. Den zweiten Geköpften behalte ich in der le des Gefässes unter Augen. Jetzt fange ich an das Gefäss 128 Ueber den Sitz der Seele dea Frosches und zu erhitzen, die steigende Temperatur des Wassers an einem : dasselbe eingesenkten Thermometer ablesend. Die Zimmertempi ratur beträgt 17i”C. Hat das Wasser aber erst die Temperatur von 25“ erlangt, li verändert sich die Scene. Dem behirnten Frosch beginnt es uj behaglich zu werden. Er verändert den Ort, steckt den Kot weit zum Wasser hinaus, und fängt an, schneller zu athmen. j höher die Temperatur steigt, desto ängstlicher werden seine B< wegungen. Verzweiflungsvoll schwimmt das gequälte Thier ij Behälter umher, bald den Kopf weit hinausstreckend und imm< geschwinder nach Kühlung jappend, bald auf den Grund d< Gefässes tauchend, um dort der Pein zu entrinnen. Die Hita nähert sich gegen 38“. Das Thier macht verzweifelte Sprüng« um aus dem Behälter zu entkommen. Es klimmt an den glatte Wänden empor und muss in das heisse Wasser zurück gestosse werden. Die immer geschwinder auf- und niederfliegenden Atb mungsmuskeln erlahmen, die Athmung setzt aus. Immer wild^ werden die Schmerzensäusserungen, und endlich bei einer Teib peratur von etwa 42“ verendet das gequälte Thier unter tetan^ sehen Krämpfen.

And the translation:

I cut off the heads of two of three frogs of the same size and attractiveness that were caught at the same time with the glowing platinum pieces of the galvanocaustic apparatus. To the I blind the eyes of those who are otherwise undamaged in order to exclude useless voluntary movements as far as possible. Then I put the last decapitated frog in a wide tin vase, the floor of which was covered with several layers of canvas and immediately bring him into the squatting position, which brain frogs always accept and then not from again ')St leave. I fill the vessel with water now, 'S only a small part of the animal protrudes from it. to I then place the blinded frog on the decapitated one, which soon also settles down in a crouching position and fearless. I'll keep the second decapitated man in the le of the vessel under the eyes. Now I start the container, the water has reached a temperature of about 25", both frogs sit still in the warm bath. On the decapitated one sees the movements of the thighs, so common in decapitated people: he might pull one thigh up a little more or straighten a zoe, movements such as those used outside of the bath Lingering second decapitated also shows, which are therefore not dependent on the increasing temperature, and which incidentally will soon stopBut once the water has reached the temperature of 25", the scene changes. The brained frog begins to get uncomfortable. He changes the place, sticks the feces far out to the water, and begins to breathe faster. j the higher the temperature rises, the more anxious his movements become. The tormented animal ij swims in despair container around, soon stretching out the head far and imm Quickly yapping for coolness, soon to the bottom d vessel to escape from the torment there. the hita approaching around 38". The animal makes desperate leaps to escape from the container. It climbs to the smooth walls and has to be thrown back into the hot water will. The respiratory muscles, which fly up and down faster and faster, become slack and breathing stops. Always wild the expressions of pain become manifest, and finally at a body temperature of about 42" the tormented animal dies with tetanic convulsions.

You can see the bits, which the translator can't cope with - these are bits which didn't transcribe well, due to being in the spine of the book and not scanned properly. I also can't read these or even make a guess at what the proper word would be in many cases, though I have fixed those that I could. However, I think that the general text is largely fine to read and easy to interpret.

Basically, what Goltz did was attempt to study the nervous system and physiology of frogs. He did this by comparing decapitated or decerebrated frogs with intact ones (apart from blinded eyes, to exclude visual stimuli). He placed both of these in room temperature water and then heated it. When heated, the decapitated frogs did not show any reflex action and would sit still until dead unless stimulated by a different stimulus, which was some mild acetic acid applied to the back of the frog (bottom of page 128, not translated here). On the other hand, intact frogs would violently try to escape and would have to be placed back into the heated container, up to about 42 C, at which point they died.

Edited to add:

On page 130, there is a passage:

Behälter einen solchen, welchem ich das Gehirn mit einem qu Schnitt dicht vor den Sehhügeln abgetrennt hatte. Zu ihm s* ich einen geköpften Frosch, welchem ich die Hinterbeine i oben geschilderten Weise verschränkt hatte. Beide Frösche bli! ganz regungslos sitzen, bis die Temperatur des Wassers 32|'* reicht hatte. Da machte der hirnbesitzende Frosch mit dem eine Bewegung nach oben und fing an schneller zu athmen. 35“ machte er mit dem Körper eine kleine Wendung und sp dann plötzlich mit einem kräftigen Satz aus dem Behälter hii In’s Wasser zurückgebracht, machte er alsbald einen zweiten Sp> aus dem Geföss. Ausserhalb desselben wiederholte er die Hi bewegungen nie, sondern verharrte nach dem einen Satz, mit ehern er das Bad verlassen hatte, in Ruhe. Nachdem er, i: wieder in’s Bad zurückgebracht, im Ganzen sechs Sprünge g' hatte, und das Wasser inzwischen allmälig eine Hitze von erlangt hatte, starb er unter tetanischen Krämpfen. Während ser Scenen hatte der Geköpfte mit verschränkten Füssen ruhi gesessen. Bei 37?“ machte er die zuckenden Bewegungen, dij aussahen, als wenn er die verschränkten Füsse auseinander bri wollte. Bald wieder beruhigt, blieb er regungslos sitzen. Ui Zeit, als der Behirnte in Krämpfe verfiel, begann bei dem ^ köpften die Wärmestarre der Muskeln. Ohne dass die v schränkten Füsse sich lösten, wurden die Schenkel | allmälig etwas nach hinten gestreckt, und das ganze Thier hart und steif.


Lately I have completed this experiment in the following way- changes; Instead of the blinded frog, I put one in the container, which I pierced the brain with a qu cut just before the brow mounds. To him a decapitated frog, whose hind legs i entangled in the manner described above. Both frogs bli! sit completely motionless until the temperature of the water is 32 had enough. Then the brain-possessing frog did that a movement upwards and began to breathe faster. 35” he made a small turn with his body and sp then suddenly with a powerful leap out of the container Brought back into the water, he immediately made a second spat from the vessel. Outside of this he never repeated the hi movements, but after one set he stayed with as soon as he had left the bath, in peace. After he had had six jumps in all when he was brought back into the bath, and the water was gradually getting hotter he died from tetanic convulsions. While The decapitated man had these scenes with crossed feet sat. At 37?” he made the twitching movements that looked like he was breaking his crossed feet apart wanted to. Soon calmed down, he sat motionless. wow Time when the crippled went into convulsions began at the beheaded the thermal rigidity of the muscles. Without the v when feet broke loose, the thighs were gradually stretched back a little, and the whole animal hard and stiff.

This is using frogs with their hind limbs crossed (and pinned?; see image page 103), so that they can no-longer swim properly and jump. The frog still gets out and is returned to water that is gradually getting hotter. Eventually it does not attempt to escape again. Note that the intact frog still tries to make movements and escape, just can't in the long run. I can only speculate on why it doesn't continue to try to escape, perhaps the water is too hot for proper function at this point, or perhaps it has learned that it can't escape, so gives up, which is a pretty sad conclusion to come to.

So, TL:DR - frogs try to escape when the water is too hot for them!

  1. Goltz F. 1869. Beitrāge zur lehre von de function der nervencentrum des frosches. Berlin.
  • $\begingroup$ Thanks for the elaborate answer! This corresponds to what Wikipedia says about Friedrich Goltz's experiment. See en.wikipedia.org/wiki/Boiling_frog#Experiments_and_analysis $\endgroup$
    – Riemann
    Mar 19, 2022 at 13:29
  • $\begingroup$ However, according to Wikipedia, Heinzmann and Fratscher got results in which a normal frog did not jump out $\endgroup$
    – Riemann
    Mar 19, 2022 at 13:30
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    $\begingroup$ @Riemann - you can track those publications down and have a look at them yourself. The author of the Wikipedia page obviously only looked at Sedgewick 1888, as they don't provide a reference for Fratscher. Heinzmann is in German, but translatable. Numerous experiments performed, but my German isn't good enough to read it, and I don't have the time to put in to translate it all. $\endgroup$
    – bob1
    Mar 20, 2022 at 20:51
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    $\begingroup$ I also haven't been able to track down Fratscher. All references come back to Sedgewick. $\endgroup$
    – bob1
    Mar 20, 2022 at 21:04

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