(Translated from Book VI., Chapter XI., of Daremberg’s French version of the works of Galen.) In his comments upon the account of the sigmoid valves which I have just quoted, Daremberg says that the description of these structures given by Erasistratus at least four hundred years earlier is admitted by Galen to be so correct that it would scarcely be possible to furnish a better one. _Galen’s Remarks upon the Subject of Diagnosis._--In the treatise entitled “On the parts of the Body Affected” (Book II., Chapter X.) Galen gives the following advice with regard to the method which it is desirable to adopt when one wishes to ascertain which part or organ is affected, what is the nature of the disease there located, and whether it is primary in its nature or secondary to some affection of earlier development:-- It should have been the special duty of Archigenes, who appeared on the scene next in order after a series of the most illustrious physicians,[42] to infuse more light into medical teaching. Unfortunately, he did the very opposite; for we who have grown old in the exercise of the art (and should therefore find it easy to comprehend what is written about medicine), are at times unable to understand what he says. Such being the true state of affairs, I now propose to undertake what Archigenes failed to accomplish. I shall commence by indicating in a general way what is the proper method to adopt when one wishes to ascertain in what part or organ the disease is located and how one should proceed when it is proposed to teach the method to others. This method may be stated in the following terms:--