It is a truth universally admitted, that the arm of physic has derived much additional power and increased energy, from the resources which are furnished by the mixture and combination of medicinal bodies. I by no means intend to insinuate that the physician cannot frequently fulfil his most important indications by the administration of one simple remedy; I only contend that, in many cases, by its scientific combination with other medicines, it will not only act with greater certainty and less inconvenience, but that its sphere of influence may be thus more widely extended, and its powers so modified or changed, as to give rise to a remedy of new powers. Such a theory is amply justified by the state of combination in which certain medicinal principles are found in our more efficient vegetable remedies, while the medicinal practice founded upon it is thus, as it were, sanctioned by Nature’s own prescriptions; enter but her laboratory, and you will soon be satisfied, that many of her potent remedies do not owe their valuable powers to any one specific ingredient, but to the combined or modified energies of various, and sometimes opposite principles. This view of the subject opens an interesting and unexplored field[239] of medical and chemical research, and I shall endeavour to avail myself of the novelties its investigation may present, and of the hints it may suggest for the improvement of _extemporaneous combination_. By contemplating the laws by which Nature effects her wise purposes, we may learn to emulate her processes, and even in some cases to correct and assist her operations:[240] such at least has been the happy result of our labours in the other departments of natural knowledge. It is said for instance that by observing the means used by nature for preventing the diffusion of light in the eye-ball, Euler derived an important hint for the improvement of his telescope; and more lately, the structure of the crystalline humour of the eye has been successfully imitated in the invention of achromatic lenses. On the other hand, it is hardly necessary to observe to what extent these instruments of art are capable of improving and multiplying the powers of that natural organ, to the contemplation of whose structure and functions, we are, as I have just stated, so greatly indebted for their origin and perfection. So shall I endeavour to shew, in the progress of this work, that the combinations of nature, as exemplified in her more valuable remedies, are capable, if properly studied, of suggesting many important hints for improving the arrangements of art; while art in return may frequently supply the defects, or extend the advantages of natural compounds. AN ANALYSIS OF THE OBJECTS TO BE OBTAINED BY MIXING AND COMBINING MEDICINAL SUBSTANCES.