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You have probably heard the phrase "canary in the coal mine". The idea of carrying a small animal underground as a living gas detector was set out by a physiologist who tested poisonous gases on himself. John Scott Haldane worked out why carbon monoxide kills, why a small animal shows the danger first, and what actually tells your brain to breathe. This post covers who he was, his main findings, the numbers from his own papers worked through, and what you can learn from him. (His son, the geneticist J. B. S. Haldane, has his own post.)
Who was J. S. Haldane?
The Gifford Lectures biography, written at the University of Glasgow, gives his birth as 3 May 1860 in Edinburgh. He graduated in medicine at Edinburgh in 1884, moved to Oxford in 1887, and studied the gases of coal mines, wells and crowded rooms. In 1896 he sent the Home Secretary a report on the causes of death in colliery explosions and underground fires. He was elected a Fellow of the Royal Society in 1897, later directed a mining research laboratory near Doncaster, and worked out "stage decompression" for Admiralty divers. He died in Oxford on the night of 14 to 15 March 1936.
Why is carbon monoxide so dangerous?
In The Action of Carbonic Oxide on Man (1895), Haldane breathed measured amounts of CO and tracked his own blood. He estimated how much haemoglobin was bound to CO by its colour: diluted normal blood looks yellow, CO-blood pink. His summary of conclusions includes:
Symptoms depend on how much of the haemoglobin is saturated with CO. They become noticeable at rest at about a third, and "urgent" at about half.
The symptoms are "due solely to deficiency in the oxygen percentage of the blood".
"The affinity of carbonic oxide for hemoglobin is about 140 times that of oxygen."
Distinct symptoms appear at about 0.05% CO in air, and urgent ones at about 0.2%.
A miner's lamp warns of other bad air, he noted, but it is "of no service in detecting small quantities of carbonic oxide".
Why does a small animal warn you first?
Haldane's answer is the surface-to-volume rule. In the 1895 paper he compares a 25 g mouse, which makes about 0.25 g of CO₂ an hour, with a 70 kg man, who makes about 40 g. Per kilogram, that is 10 g for the mouse against about half a gram for the man, so gas exchange in the mouse's lungs is "about 20 times as rapid". A mouse in poisonous air is affected about 20 times sooner than a person, leaving time to get out.
He had already tried this in Staffordshire collieries, where mice "gave timely warning". In The Investigation of Mine Air (1905), the author of that section writes that he "proposed the plan of making use of a small warm-blooded animal (a mouse or very small bird) as an indicator of CO", and warns that the test "is not a very delicate one". The canary is the bird that became famous; in Haldane's own papers, the mouse comes first.
Worked example: how much haemoglobin does CO take?
In his sixth conclusion, Haldane says the CO the blood can take up depends on the relative affinities of the two gases for haemoglobin and on their relative pressures. As a formula: CO-haemoglobin / oxygen-haemoglobin = affinity ratio × (CO pressure / O₂ pressure). He gives the arterial oxygen pressure as about 16% of an atmosphere.
Air with 0.05% CO. Ratio = 140 × (0.05 / 16) = 0.44. The fraction of haemoglobin carrying CO is 0.44 / (1 + 0.44) = 0.30, about a third.
Air with 0.2% CO. Ratio = 140 × (0.2 / 16) = 1.75. Fraction = 1.75 / 2.75 = 0.64, more than half.
Check against his symptoms. A third saturated is where he felt symptoms at rest; half is where they became urgent. His affinity, his oxygen pressure and his symptom thresholds agree.
Common mistake: thinking CO harms by using up oxygen in the air. At 0.2%, the air still holds almost all its oxygen. CO harms by occupying haemoglobin.
What tells you to breathe?
In The Regulation of the Lung-Ventilation (1905), Haldane and John Gillies Priestley sampled the air at the end of a breath, from deep in the lungs. They concluded that "the regulation of the lung-ventilation depends on the pressure of CO₂ in the alveolar air", and that a rise of 0.2% of an atmosphere in alveolar CO₂ "was sufficient to double the ventilation".
Numbers. At 760 mm Hg, Haldane's resting alveolar CO₂ of 5.6% is about 42.6 mm Hg. A rise of 0.2% of an atmosphere is just 1.5 mm Hg, yet it doubles breathing. During their exercise tests, ventilation rose "in exact proportion" to the extra CO₂ produced, keeping alveolar CO₂ almost constant.
In 1914, with Johanne Christiansen and C. G. Douglas, he showed that blood without oxygen takes up considerably more CO₂ than oxygenated blood, so loading oxygen in the lungs helps unload CO₂. This is now called the Haldane effect. Our post on breathing and exchange of gases covers how this fits the NEET syllabus.
To revise these ideas one concept at a time, the Fermi Concept Library covers every concept in physics, chemistry, biology, mathematics and computing.
What can a student take from how he worked?
Measure the thing that matters. He tracked haemoglobin saturation, not just symptoms.
Check your numbers against each other. His affinity and his symptom thresholds agree, as the worked example shows.
Take science to where people are at risk. Collieries, diving and war gases were his laboratories. His self-experiments were dangerous; do not copy them.
Next step: use Haldane's numbers to find the CO percentage that would bind half the haemoglobin, and compare it with his "urgent" threshold.
