CHAPTER XIII

THE ENGLISH AND FRENCH CHEMISTS CONTRIBUTE THEIR SHARE TOWARD THE ADVANCE OF MEDICAL KNOWLEDGE

During the latter part of the eighteenth century the chemists of England and France manifested a new and decidedly stronger interest in their branch of natural science; indeed, they seemed to have suddenly appreciated the fact that observation and experience afforded the only route by which they might secure a genuine and useful increase of their stock of knowledge. In the departments of physiology and pathology, for example,—not to mention also that of therapeutics,—there were at that period many questions which still remained unsettled and which could not be satisfactorily answered until a further advance had been made in the existing knowledge of chemistry. Hence the great importance of the movement to which I have just referred. To cite only one of these unsettled questions I will mention here that relating to the nature of the change which occurs in the blood when it loses its venous hue after passing through the lungs, and also, vice versa, when it loses its arterial color after passing through the tissues in other parts of the body. Harvey’s discovery had gone no further than to reveal the pathway of the blood in its winding course throughout the body, but now physiology demanded an explanation of the changes which this fluid undergoes in its travels along that pathway. The answer to this last question, as will now be shown, was not gained through the efforts of a single individual but by the researches that were made by several very able English and French scientists, more particularly by Joseph Priestley, the English chemist, and by Lavoisier, the French biologist and chemist. During the preceding fifty or sixty years the physicians of Europe had been obliged, for want of a more satisfactory explanation, to accept Stahl’s phlogiston theory (that all combustible materials contain an element to which he applied the name of “phlogiston”), at least as a basis or starting-point for the desired explanation.

Joseph Priestley, who was born at Fieldhead, near Leeds, England, in 1733, received his early education at a Dissenting school; and in 1755 he became a Dissenting minister at Needham Market. So far as the available evidence affords any clear indication of Priestley’s bent of character the inference is permissible that he was first and chiefly a scientist, but yet possessing a profoundly religious type of mind which the influences surrounding his boyhood doubtless helped to intensify. Thus, during his ministerial work he managed to devote a large part of his time to original investigations in the domain of chemistry; and, as early as in the year 1774, he succeeded in obtaining a gaseous product to which he gave the name of “dephlogisticated air.”[[16]] A detailed description of this discovery of oxygen—the name which was given to the new gas at a later date—will be found in Vol. 2 of the second edition of Priestley’s “Experiments and Observations on Different Kinds of Air,” London, 1784. Broadly speaking, Priestley obtained the new product by heating the red oxide of mercury. Subsequently he discovered that respiration took place more easily, and that combustion progressed more actively, in the presence of this gas. But it is to the French chemist Lavoisier that we owe the knowledge of the full significance of oxygen. On the other hand, it was the English chemist Cavendish who confirmed Priestley’s discovery that atmospheric air is composed of water and different acids. Lavoisier, it is claimed, discovered that all the acids which he examined contain oxygen.

Speaking, at a later date, of his attempt to produce a work on the chemistry of the air, Priestley says: “I find it absolutely impossible to produce such a work that shall be anything like complete. My first publication I acknowledged to be very imperfect, and the present, I am as ready to acknowledge, is still more so. But, paradoxical as it may seem, this will ever be the case in the progress of natural science, so long as the works of God are, like himself, infinite and inexhaustible. In completing one discovery we never fail to get an imperfect knowledge of others, of which we could have no idea before; so that we cannot solve one doubt without creating several new ones. Travelling on this ground resembles Pope’s description of travelling among the Alps, with this difference, that here there is not only a succession, but an increase of new objects and new difficulties.”

Here is the description to which Priestley refers:—

So, pleas’d at first the tow’ring Alps we try,

Mount o’er the vales, and seem to tread the sky.