[7] The whimsical "_doctrine of signatures_" which prevailed in the middle ages, and had its origin from very remote times, serves at least to show that the local tendencies of medicines have always been more or less recognised. So slight an experience is sufficient to demonstrate their existence, that it could indeed hardly be otherwise. It was oddly supposed that every natural substance bore evidence in its outward form or physical peculiarities of the part of the system over which it exerted a curative power. [8] "He was one of the first who, leaving the old conjectural method of physical writers, struck into a new and more solid way of reasoning, grounded upon observations and mathematical principles."-- _Preface to Dr. Pitcairn's Works: 1715_. [9] "A Treatise of Diseases in General, wherein the true causes, natures, and essences of all the principal diseases incident to the human body, are mechanically accounted for and explained, and their respective intentions of cure assigned upon the same principles," vol. ii. p. 813, 820. [10] "Medical Precepts and Cautions," page 294. [11] "If there be any bodies--suppose gold and silver--out of which all these principles cannot be drawn, let not the artist think that it is because they are not therein contained. No! it is because that God has so firmly united them against the possibility of our separation."--P. 809. [12] Dr. Pitcairn's Works, 1715, p. 219. [13] I have omitted here to make mention of the doctrine of infinitesimal doses, not only because it is out of my province, but because it is really too unreasonable to be even discussed. When it is said that the decillionth of a grain--the ordinary dose among these practitioners--is expressed by a fraction, the denominator of which is a unit followed by sixty ciphers, this statement will be surely enough for any man who is at all acquainted with figures. I do not conceive it possible that matter is _divisible_ to any thing like this extent. [14] Sydenham's Works, translated from the Latin by Dr. Swan. 5th edition, 1769, p. 1. [15] Preface to the same, p. 22. [16] "First Lines of the Practice of Physic." Fourth edition, 1784. Vol. i. p. 126 et seq. [17] An exception should be made here of certain animal poisons, such as the venom of serpents, which, though they act on the system when introduced directly into the blood, seems to be rendered innocuous by the action of the stomach, which probably decomposes them. [18] Physiological Researches, p. 63-67. [19] It should be mentioned that Sir Benjamin Brodie, though admitting the force of the above experiments, and deriving from them very similar inferences, yet considers it likely that the action of a medicine or poison may be _partly_ propagated by means of the nervous system. _Op. cit._ p. 127. [20] _Vide_ Paper in Medical Gazette, June 18th, 1841. [21] Todd and Bowman's Physiology, vol. ii. p. 280. [22] _Vide_ Pereira's Materia Medica, vol. i. pp. 101, 106.