by Frank I. Katch
INDEX	Santorio experiments breakthrough in energy metabolism

Lavoisier ushered in modern concepts in metabolism, nutrition, and exercise physiology. More has been written about Lavoisier than of his worthy contemporaries Black, Priestley, Cavendish, and Hales for one simple reason: his discoveries in respiration chemistry and human nutrition were as essential as William Harvey's were to circulatory physiology and medicine. A Paris monument summarizes Lavoisier's contributions:

Analysis and Synthesis of Air--Composition of Oxides and Acids--Composition of Water--Theory of Combustion--Respiration and Animal Heat--Permanence of Weight of Matter and Simple Substances- -Imponderable Nature of Heat and Its Role in Chemistry.

The accomplishments most germane to Exercise Nutrition pertain to respiratory chemistry and exercise metabolism. Lavoisier knew of Scheele's experiment with bees from correspondence in 1774. Three years later, Lavoisier used accurate balance scales^* to determine what Scheele, Priestly, and others could not explain: an animal in a closed chamber consumed "air eminently respirable" (oxygŽne) and produced "a‘riform calcic acid" (carbon dioxide). Lavoisier noted:

...that if after an animal had perished in a confined space and the carbon dioxide in the atmosphere was absorbed by alkali the "foul air" remaining was the same kind of air as that found after metals had been calcined in air in an inclosed space. All the former qualities of this air could be restored by adding to it "air eminently respirable."

Lavoisier's respiration experiments invalidated the phlogiston theory despite protestations from Priestley and Scheele. Lavoisier collaborated with French mathematician Pierre Simon de Laplace (1749 -1827) on problems in respiration chemistry. Their vital experiments with guinea pigs in 1780 first quantified the oxygen consumed and carbon dioxide produced by metabolism. Over a ten-hour period, they collected approximately 3 g of carbonic acid from an animal breathing oxygen. In a second experiment, they placed a guinea pig into a wire cage, which in turn was placed into a double-walled container. Ice packed into the double walls of the outer container maintained a constant temperature; ice between the cage and the inner wall of the container melted because of the animal's body heat. During 24 hours 13 oz. (370 g) of ice melted. Lavoisier and Laplace concluded that the total heat produced by the animal equaled the amount heat required to melt ice. In their own words:^**

Thus, one can look at heat produced during respiration by the transformation of humid air into dry air, as the principle cause of animal heat conservation and if other causes intervene, their effect is negligible.
Respiration is thus a very slow combustion phenomenon, very similar to that of coal; it is conducted inside the lungs, not giving off light, since the fire matter is absorbed by the humidity of the organs of the lungs. Heat developed by this combustion goes into the blood vessels which pass through the lungs and which subsequently flow into the entire animal body. Thus, air that we breathe is used to conserve our bodies in two fashions: it removes from the blood fixed air, which can be very harmful when abundant; and heat which enters our lungs from this phenomenon replaces the heat lost in the atmosphere and from surrounding bodies.
...animal heat conservation is thus largely attributable to heat produced by the combination of humid air inspired by the animals and dry air in the blood vessels.

Original ice calorimeter used by Lavoisier and LaPlace.	Lavoisier and his friend, the famous chemist Berthollet, in Lavoisier's laboratory.

In this experiment, Lavoisier decomposed water over iron in a specially designed burning stove, capturing the end products.

Lavoisier, extremely wealthy and influential, often was depicted in newspaper cartoons. In this spoof, Lavoisier and Humphry Davey, another influential scientist, administer one of Lavoisier's concoctions (oxygen) to their French leader Napoleon.

With his colleague, the chemist Armand Séguin (1767-1835), Lavoisier studied the influence of muscular work on metabolism. A contemporary painting shows the seated Séguin as he depresses a pedal while a copper mask captures the expired air. A physician takes Séguin's pulse to determine the separate effects of exercise and food consumption. (For several hours before the experiment, Séguin had abstained from food.) Resting energy metabolism without food in a cold environment increased by 10%; it increased 50% due solely to food; 200% with exercise; and 300% by combining food intake with exercise.

Lavoisier and Séguin also observed that oxygen consumption, pulse rate, and respiratory rate increased during work.

Consequently, from the experiments conducted on Mr. Séguin, it results that a fasted man in a state of rest and in 26 degrees of temperature, divided into 80 parts, consumes 1210 cubic inches (24 litres) of vital air; it also results that this consumption increases in a cold environment and that the same man, fasted and resting, in 12 degrees of temperature, consumes 1344 cubic inches (27 litres) of vital air. During digestion, this process is increased to 1800 or 1900 cubic inches (38 litres). All these values are increased during movement and exercise. Mr. Séguin, fasted and carrying a weight of 15 pounds (7 kg) on a distance of 613 feet (200 metres), consumed 800 cubic inches of air, e.g. 3200 cubic inches (63 litres) per hour. Lastly, when the same exercise was done during digestion, the quantity of vital air consumed reached a value of 4600 cubic inches (91 litres). The exercise performed by Mr. SŽguin involved carrying a 15 pound weight (7 kg) over a distance of 650 feet (211 metres) during 15 minutes.

Lavoisier and Séguin connected two essential components of physiology--external respiration and internal combustion (heat production). This linkage proved that oxidative processes (combustion) were affected not only by food intake, but also by temperature and mechanical work. Atmospheric air provided oxygen for animal respiration. Furthermore, the "caloric" (now known as heat) was liberated in metabolism. Formerly, a vital flame" was said to burn within the heart itself; now respiration, the "substance of the animal itself," provided the necessary ingredients for combustion.

In 1837, the German physiologist Heinrich Gustave Magnus (1802 -1870) first analyzed blood and corrected one flaw in Lavoisier's explanation. The Frenchman assumed that hydrogen and carbon were oxygenated in the lungs. Magnus argued that combustion must occur throughout the body, and not just in the lungs. His famous experiments showed that both carbon dioxide and oxygen existed in arterial and venous blood. Because there was more oxygen in arterial blood, Magnus deduced that the lungs could not be the primary site of combustion.

In addition to studying respiration, Lavoisier conducted research in nutrition.¹ Already knowing that animal tissues contained nitrogen, he investigated the composition of isolated plant fractions and concluded that combinations of carbon, hydrogen, and oxygen alone constituted sugars, gums, and starches.

Noting that France's food supplies were becoming depleted, Lavoisier reported in 1778 to the Academy of Sciences on practical methods to measure wheat and flour. He wrote:

It has to be accepted that other grains such as barley and oats, which do not contain gluten, are also nutritious. Starch must therefore be nutritious, but Parmentier seems to us to go too far in singling out starch as the only nutritive element in wheat. It seems obvious that gluten, with its chemical properties, is more 'animalized' and therefore eminently nutritive.

Lavoisier paved the way for future studies of energy balance by recognizing for the first time that the elements involved in metabolism (carbon, hydrogen, nitrogen, and oxygen) appeared neither suddenly nor disappeared mysteriously. Rather, they reconfigured themselves in a predictable sequence during combustion. He supplied basic truths: only oxygen participates in animal respiration, and the "caloric" liberated during respiration is itself the source of the combustion.

These discoveries, fundamental to modern concepts of energy balance, could not protect Lavoisier from the intolerance of his revolutionary countryman. He was beheaded by the Jacobin tribunal in 1794. Yet once more, thoughtless resistance to innovative science temporarily delayed the triumph of truth.

© Frank I. Katch, William D. McArdle, Victor L. Katch. 1998.

^*A collection of Lavoisier's instruments are in the Conservatoire des Arts et Metiers in Paris. One of the balances could weigh 600 mg to ± 5 mg, and another was accurate to the nearest ± 0.1 mg.

^**Translation provided by Pierre P. Lagasse, Ph.D., Physical Activity Sciences Laboratory. School of Medicine. University of Laval, Quebec, Canada.

References

1. Carpenter, K. J.(1994). Protein and energy: a study of changing ideas in nutrition. Cambridge University Press, London.

Additional Resources

Duveen, D. I., and Klickstein, H. S. (1954). A Bibliography of the Works of Antoine Laurent Lavoisier, 1743-1794. London: W. Dawson & Sons, and E. Weil.

Guerlac, H. (1973). "Lavoisier," Dictionary of Scientific Biography, Vol. VIII, Bibliography, pp. 87-91.

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