arrived at a fairly accurate conception of the important part played by these particles in the processes of life. He recognized that the substance embodied in these particles "formed only a part of the atmosphere, that it was essential for burning, that it was essential for all the chemical changes on which life depends, that it was absorbed into the blood from the lungs, carried by the blood to the tissues, and in the tissues was the pivot, the essential factor of the chemical changes by which the vital activities of this or that tissue are manifested. It was essential in muscle to the occurrence of muscular contractions, it was essential in the brain to the development of animal spirits. This great truth was reached at a time when the men of chemistry were struggling with the spiritualistic fermentations of van Helmont on the one hand, and with the material effervescences of Sylvius on the other. It was reached by a young man of twenty-five years, who died a few years afterwards."[1]
For nearly a hundred years this fundamental idea so skillfully worked out lay practically dormant and no material progress was made until, in the latter part of the eighteenth century, Priestley prepared his dephlogisticated air and Lavoisier discovered oxygen. Then came essentially a revival of Mayow's views concerning respiration, only with a clearer understanding of the nature of the process. As stated by Lavoisier and Laplace, "respiration is a combustion, slow it is true, but otherwise perfectly similar to the combustion of charcoal. It takes place in the interior of the lung without giving rise to sensible light because the matter of the fire (the caloric) as soon as it is set free, is forthwith absorbed by the humidity of these organs. The heat developed by this combustion is communicated to the blood which is traversing the lungs and from the lungs is distributed over the whole animal system."[2]
In this conception of so-called respiration the fundamental errors as viewed from the standpoint of to-day are first: the idea that the process deals solely with the combustion of carbon and secondly, that the process is limited to the lungs where a hydrocarbonous fluid was supposed to be secreted, i. e., from or through the tubes of the lungs. Later, Lavoisier himself recognized that in this process of combustion in the animal body hydrogen (discovered by Cavendish in 1781) was likewise involved, and that water as well as carbon dioxide was a normal product of the oxidation that is associated with respiration. Still later, the Italian investigator, Spallanzani, through his experiments on animals broadened the conceptions then prevailing by proving that the individual tissues of the body, like the organism as a whole, respire, i. e., that they consume oxygen and produce carbon dioxide. This
