Such figures are exceedingly useful, when access annot be had to the parts of the body which they repre sent ; but to be contented with studying figures when the originals may be procured, not only bespeaks a total want of taste for anatomy, but seems scarcely- consistent with common understanding.
The use of the microscope, which was introduced about the middle of the 16th century, was another great acquisition to anatomy. It was first tried by the accurate Eustachius, and afterwards employed by Grew and Mal pighi in illustrating the structure and economy of plants. Malpighi also made use of it in demonstrating parts of the animal system. To this instrument we are indebted for many discoveries of Swammerdam, Leewcnhoek, Baker, Trembley, Lyonet, and Bonnet. It has given rise, likewise, to sonic foolish and absurd theories, which are evidently founded on optical deceptions : we allude, particularly, to a theory ul animakula in the seminal fluid ; another of muscular motion, founded on the struc ture of the ultimate fibre ; and a third, about the struc ture and appearance of the nerves.
The last improvement of this kind which deserves to be mentioned, is the art of injection. To dissect pro perly the smaller branches of collapsed blood-vessels, had always been found a difficult and tedious operation. As a remedy fur this inconvenience, Jacobus Sylviu5, the master of Vesalius, was wont to fill them with a co loured liquor ; Eustachius adopted a similar plan while examining the kidnies ; and the same method was occa sionally practised by Glisson, Bellini, Willis, and others ; while Riolan was accustomed to inflate them with air. Among those who have improved this mode of demon stration, the honourable Mr Boyle deserves particularly to be mentioned. He had seen some dried preparations,• and proposes different kinds of injections, that would af terwards harden and preserve the veins and arteries plump. Portal informs us, that something of this kind was employed by Bellini ; at last De Graaf, about the year 1964, contrived convenient instruments for the pur pose, and claimed the merit of the whole discovery.f What now remained to be sought was a proper injec tion. Marcellus Malpighi had employed quicksilver ;
and De Graaf only mentions a number of tinctures, which all flowed out on the least rupture of the vessels. Ifis countryman Swammerdam, seeing the defect, em ployed wax,which hardens upon cooling ; and, to secure the praise of the invention, sent one of his preparations to the Royal Society of London in 1672. Ruysch, the friend of Swammerdam, carried this art to the highest perfection which it has yet attained ; made a number of valuable discoveries ; and, by means of maceration and erosion, exhibited large clusters of vessels as small as hairs, and freed from every surrounding substance.
Having thus given a general view of the discoveries made in anatomy by means of dissection and obserVation, we shall proceed to examine the advantages which it has derived from the application of mechanical and chemical philosophy, and to inquire how far those sciences may enable us to explain the phenomena of organized bo dies.
The ancients could conceive no other method of ex plaining the appearances of material objects than by me chanical philosophy. So partial was Pythagoras to this science, that, even in morals and theology, he employs the language of geometry. Hippocrates himself, if the letter to Thessalus be genuine, has strongly recommend ed geometry and numbers to the surgeon and physician, and mentioned the cases in which they may be useful. Plato imagined that the Deity himself was always geo metrizing ; and has asserted, that the four elements are four regular geometrical figures. Galen endea voured to account for a number of diseases from certain changes in the number, magnitude, figure, situation, ve locity, momentum, and adhesion of the parts ; while Descartes, an eminent philosopher and mathematiciar, biassed by a favourite hypothesis, was led to infer, that inferior animals are mere machines. Such opinions seemed not only to warrant, but even to invite the appli cation of geometry in explaining the functions of the animal structure. Accordingly Fabricius ab Aquapen dente partially applied mathematical reasoning to illus trate the action of some of the muscles.