In therapeutics he very early laid down the fundamental maxim that every disease must be combated by contrary remedies, justifying this by every species of argument, amounting to this: that every disease must be combated by its contrary because all that cures a disease is contrary to it. This was, in part, the doctrine of "_Contraria contrariis curantur_"--the antithesis of the equally absurd sophism: "_Similia similibus curantur_" which three hundred years later was erected into an excuse for the foundation of an{118} alleged new school. There can be no doubt that Fernel rendered very great service to his time and to subsequent generations, despite the fact that his recommendations and statements were too often founded upon sophistry. Just here we must digress for a moment to consider the status of bleeding. Hippocrates and Galen had advised to bleed largely from the arm on the affected side in pleurisy and pneumonia. That practice was gradually abandoned as Greek traditions were lost sight of, and finally the Arabs substituted for it something entirely different,--namely, pricking a vein in the foot in order to let blood flow drop by drop. Their method prevailed throughout Europe until the commencement of the sixteenth century, or about the time when Fernel appeared upon the scene. A Parisian physician named Brissot had revived the ancient (the Greek) practice during an epidemic of pleurisy, and had obtained thereby astonishing success, which he hastened to publish, commending the method employed. He thus created a great uproar in the medical world. The innovation found foes and defenders, and disputes grew warm, even to the fever point. Finally, the ancient method was generally revived, and Fernel accepted it. Felix Plater was born in 1536, in Basel, Switzerland, and died in 1614. He had several sons who made their mark in medicine. In his large work, which preceded that of Fernel, he took perhaps the first step in an unexplored route,--namely, in the classification of disease _according to the totality of apparent symptoms_. Defective as this classification appears in our eyes, its author lived a long life as a very distinguished practitioner and professor in his native town. Giovanni Batista Porta was born in Naples in 1536, traveled extensively in Italy, France, and Spain, and founded in 1560 an Academy of the Segreti. He was accused of magic, and was compelled to refute the charges in Rome.{119} He died in 1615, having been one of the leading scientists of his time, and the founder of modern optics. In the first edition of his _Magia Naturalis_, published in Naples, 1587, is found the first description of the camera obscura,--of course, in a very incomplete form and without lenses.