The system of Dr. Boerhaave then governed the practice of every physician in Philadelphia. Of course diseases were ascribed to morbid acrimonies, and other matters in the blood, and the practice of those years was influenced by a belief in them. Medicines were prescribed to thin, and to incrassate the blood, and diet drinks were administered in large quantities, in order to alter its qualities. Great reliance was placed upon the powers of nature, and critical days were expected with solicitude, in order to observe the discharge of the morbid cause of fevers from the system. This matter was looked for chiefly in the urine, and glasses to retain it were a necessary part of the furniture of every sick room. To ensure the discharge of the supposed morbid matter of fevers through the pores, patients were confined to their beds, and fresh, with cool air, often excluded by close doors and curtains. The medicines to promote sweats were generally of a feeble nature. The spiritus mindereri, and the spirit of sweet nitre were in daily use for that purpose. In dangerous cases, saffron and Virginia snake-root were added to them. Blood-letting was used plentifully in pleurisies and rheumatisms, but sparingly in all other diseases. Blood was often drawn from the feet, in order to excite a revulsion of disease from the superior parts of the body. It was considered as unsafe, at that time, to bleed during the monthly disease of the female sex. Purges or vomits began the cure of all febrile diseases, but as the principal dependence was placed upon sweating medicines, those powerful remedies were seldom repeated in the subsequent stages of fevers. To this remark there was a general exception in the yellow fever of 1762. Small doses of glauber's salts were given every day after bleeding, so as to promote a gentle, but constant discharge from the bowels. The bark was administered freely in intermittents. The prejudices against it at that time were so general among the common people, that it was often necessary to disguise it. An opinion prevailed among them, that it lay in their bones, and that it disposed them to take cold. It was seldom given in the low and gangrenous states of fever, when they were not attended with remissions. The use of opium was confined chiefly to ease pain, to compose a cough, and to restrain preternatural discharges from the body. Such were the prejudices against it, that it was often necessary to conceal it in other medicines. It was rarely taken without the advice of a physician.