Much yet remains to be known upon this subject. I have mentioned the different states of the pulse, which call for bleeding, but it is more difficult to know when to prescribe it, when the pulse imparts no sign of disease. In general it may be remarked, where the disease is _recent_, the part affected important to life, and incapable of sustaining violent morbid action long, without danger of disorganization, where pain is great, and respiration difficult, the pulse may be disregarded in the use of the lancet. But to return. II. Regard should be had to the character of the reigning epidemic, in deciding upon blood-letting. If the prevailing fever be of a highly inflammatory nature, bleeding may be used with more safety, in cases where the indications of it from the pulse are somewhat doubtful. The character of a previous epidemic should likewise direct the use of the lancet. The pestilential fever which followed the plague in London, in 1665, Dr. Sydenham says, yielded only to blood-letting. It is equally necessary in all the febrile diseases which succeed malignant fevers. III. Regard should be had to the weather and season of the year. Dr. Hillary and Dr. Huxham both say it is much more necessary in dry, than in wet weather, and, all physicians know, it is more copiously indicated in the spring and autumn, than in summer and winter. IV. The constitution of a patient, and more especially his habits with respect to blood-letting, should be taken into consideration, in prescribing it. If he be plethoric, and accustomed to bleeding in former indispositions, it will be more necessary, than in opposite states and habits of the system. Nature will expect it. V. The corpulency of a patient should regulate the use of the lancet. A butcher of great observation informed me, that a fat ox did not yield more than from one half, to one third of the quantity of blood of a lean one, of the same size of bone, and it is well known, that the loss of a small quantity of blood, after cutting off the head of a fowl, is always a sign of its being fit for the table. The pressure of fat upon the blood-vessels produces the same effects in the human species that it does in those animals; of course, less blood should be drawn from fat, than from lean people, under equal circumstances of disease. VI. As persons have more or less blood in their vessels, according to their size, less blood should be drawn, under equal circumstances, from small than large people.