Such a comparison with the work of a contemporary teacher in the same town shows how immeasurable was the advance made by Harvey. It only remains to show what has been done since his death to perfect our knowledge of the heart and of the circulation. The use of the microscope by Malpighi in 1661 gave an insight into the true nature of the porosities by which the blood passed from the terminal arteries to the commencing veins in the lungs and proved them to be vessels. The capillary circulation was still further investigated by Leeuwenhoek in 1674 who described it as it is seen in the web of a frog’s foot, and in other transparent membranes; Blankaart in 1676, William Cowper in 1697, and afterwards Ruysch, studied the arrangement of the capillaries by means of injection. In 1664 Stenson demonstrated that the heart was a purely muscular organ.
The various histological details being thus settled there came a long interval until chemistry was sufficiently advanced to enable definite statements to be made about the aëration of the blood.
The work of Black in 1757 and of Priestley and others in 1774 and 1775 at last allowed the process of respiration and the true function of the lungs to be explained upon scientific grounds. But the interval between the discovery of the capillaries and the explanation of the act of respiration was not wholly barren; for in 1732 Archdeacon Hales, by means of experiments, obtained an important insight into the hydraulics of the circulation. During the present century our knowledge of the physics of the heart and circulation has been reduced almost to an exact science by the labours of the German, French, and Cambridge schools of physiology under the guidance respectively of Ludwig, of Chauveau, and of Foster; whilst the nervous mechanism of the heart and of the arteries has been thoroughly investigated by Gaskell and others.
CHAPTER IX
The Treatise on Development
Fuller, speaking of Harvey, says very ingeniously: “The Doctor though living a Bachelor, may be said to have left three hopeful sons to posterity: his books,
“1. De circulatione sanguinis, which I may call his son and heir: the Doctor living to see it at full age and generally received.
“2. De generatione, as yet in its minority: but I assure you growing up apace into public credit.
“3. De ovo, as yet in the nonage thereof; but infants may be men in due time.”