According to the OED of etymology, the first recorded use of the term guinea pig in a scientific context dates from the 1920s. However, the following description of the work of Lavoisier and Laplace clearly antedates that usage: link to original
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:
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.
Lavoisier's ideas were radical for 1780 because they connected heat, work, and energy.