“ Son George,” Sir Henry Colt wrote his progeny in the summer of 1631, “ I have taken pains day and night to collect this journal … because if you will prove a seaman and undertake voyages [to the New World] you may learn how to employ your time at sea, and who to thank for your conservation.” Appended to the diary were “ some rules for diet and health … the way being dangerous because of the change in climates, especially about the tropics.” Among other things, Sir Henry cautioned the younger Colt that he would find the “ torrid zone or middle region temperate enough,” but the most dangerous place would be the “ tropics under which you must pass for pestilent fevers … which have killed many in the hot season of year.” To reduce the possibility of sickness which was likely to occur as a result of travel into warm climates, Colt prescribed some precautionary measures.
Sir Henry Colt lived in an age when such modern terms and concepts as anopheles mosquito, malaria, yellow fever, and immunization zones had little or no meaning. In his day, physicians had not established a connection between anopheles mosquito and malaria, or aedes mosquito and yellow fever. When counseling his son on how to remain healthy in the Americas, Colt had no reason to warn him that anopheles and aedes mosquitoes often served as hosts for parasites which were deadly to human beings, and hence the bites of these insects could be dangerous.
Colt and his contemporaries did, however, hold coherent medical views about disease and its origins which informed their behavior in the New World.