Johnson’s friend, the surgeon Dr Staunton, was about to leave for the West Indies when he received this advice in a letter from Johnson. America here includes the Islands; New England was still a collection of British colonies. I hope you have the chance to enjoy examining something on holiday, a natural or even man-made curiosity.
In America there is little to be observed except natural curiosities. The new world must have many vegetables and animals with which philosophers are but little acquainted. I hope you will furnish yourself with some books of natural history, and some glasses and other instruments of observation. Trust as little as you can to report; examine all you can by your own senses. I do not doubt but you will be able to add much to knowledge, and, perhaps, to medicine. Wild nations trust to simples; and, perhaps, the Peruvian bark is not the only specifick which those extensive regions may afford us.
Life of Johnson, Volume 1 1709-1765 by James Boswell.
Cortex peruvianus study by Antonie van Leeuwenhoek, 1706; better known today as quinine. A simple is a plant-based medicine; a specific is a medicine for a particular disease; in this case malaria.