What conclusion is to be drawn from this fact? Have those who reproach the science of physiology with being only a tissue of contradictions and errors ever opened a book on physiology (for example, the text-book of Schaefer, in two large, compact, closely written volumes of 1000 pages each)? They would there find thousands of positive, incontestable facts on all the questions which concern physiology.
Let us take, each in its turn, the great functions of life, and we shall see that they have become known only by experimentation.
1. _The Circulation of the Blood_, suspected by Michel Servet, Realdo Colombo, and Andreas Cesalpin, was really established by Harvey in 1628.
Yet Harvey was only able to demonstrate it by experiments performed on the living bodies of frogs and deer. Since Harvey's time, the laws of the circulation have been established with admirable precision. Hales demonstrated the pressure of blood in the vessels. Chauveau and Marey introduced into the heart of a horse an apparatus which enabled the pressure of the blood in the heart, in the arteries, and in the veins, to be measured. Weber found that the pneumogastric nerve stopped the heart's action. Ludwig applied the graphic method to the circulation. Delicate instruments have been constructed which give diagrams of the pulsations and measure the pressure of the blood in the arteries and in the heart of man. Claude Bernard discovered the nerves which regulate the movements of the vessel walls. In short, the whole history of the circulation is due solely to vivisections, and it would be ridiculous to speak of our uncertainties in this respect; for the essential mechanical or nervous laws of the circulation are as well known now as those of the combinations of nitrogen with oxygen.
2. _The Respiration_ remained profoundly unknown, as to its inmost nature, right up to Lavoisier's time. Lavoisier placed some guinea-pigs in a box filled with ice, measured the quantity of heat thrown off, the quantity of oxygen consumed, the quantity of carbonic acid produced; and he was thus able to deduce a fundamental law of life, viz., that life is essentially combustion. He made experiments on himself also; but however great one's respect for the life of a guinea-pig may be, must it be considered wrong that Lavoisier should have experimented on the guinea-pig before experimenting on himself?
