Birth of the guinea pig.

Main Entry: guinea pig

Function: noun

Date: 1664

1 : a small stout-bodied short-eared tailless domesticated rodent (Cavia porcellus) of South American origin often kept as a pet and widely used in biological research —called also cavy

2 : a subject of research, experimentation, or testing

The original research guinea pig played a significant role in the history of biology; it led to the discovery that mammalian respiration is the same as combustion. In the 1650 century Otto von Guericke invented the air or vacuum pump and launched a new era of experiments into the nature of air, most notably by Robert Boyle. Boyle and others placed burning candles and small animals into bell jars and pumped out the air extinguishing the candles and suffocating the animals. Both Boyle and the Englishman John Mayow realised that there must be some sort of connection or relationship between combustion and respiration but what this might be they could not say. The main reason for their inability to solve the problem was that for all of the researchers in the 17^th century air was still regarded as a single substance and not as the mixture of gases that we now know constitute its makeup.

During the 18^th century various researchers, most notably Joseph Black in Scotland and Henry Cavendish and Joseph Priestley in England, managed to separate and identify various gases such as burning air (hydrogen), fixed air (carbon dioxide) and oxygen. Building on this work the Frenchman, Lavoisier, was able to show that combustion was the oxidation of flammable substances, which usually led to the production of carbon dioxide.

Lavoisier, together with Simon Laplace (yes that Laplace!), then devised an ingenious experiment to demonstrate that respiration is combustion. They built a calorimeter to measure the heat of combustion generated by respiration. They placed a guinea pig in a respiration chamber inside a closed vessel filled with snow. They then pumped air into the respiration chamber and measured the volume of melted snow that flowed out of the surrounding vessel. This enabled them to calculate the heat generated by the guinea pig’s respiration.

As well as being the star of a great moment in the history of physiology the guinea pig gave his name to the class of experimental subjects.