The simplest and most direct definition of syphilis is that it is a contagious constitutional disease, due to a germ, running a prolonged course, and at one time or another in that course is capable of affecting nearly every part of the body. One of the most important parts of this rather abstract statement is that which relates to the germ. To be able to put one's finger so definitely on the cause of syphilis is an advantage which cannot be overestimated. More than in almost any other disease the identification of syphilis at its very outset depends upon the seeing of the germ that causes it in the discharge from the sore or pimple which is the first evidence of syphilis on the body. On our ability to recognize the disease as syphilis in the first few days of its course depends the greatest hope of cure. On the recognition of the germ in the tissues and fluids of the body has depended our knowledge of the real extent and ravages of the disease. With the knowledge that the germ was related to certain other more familiar forms, Ehrlich set the trap for it that culminated in salvarsan, or "606," the powerful drug used in the modern treatment. By the finding of this same germ in the nervous system in locomotor ataxia and general paralysis of the insane, the last lingering doubt of their syphilitic character was dispelled. Every day and hour the man who deals with syphilis in accordance with the best modern practice brings to bear knowledge that arises from our knowledge of the germ cause of syphilis. No single fact except perhaps the knowledge that certain animals (monkeys and rabbits especially) could be infected with it has been of such immense practical utility in developing our power to deal with it. The germ of syphilis,[3] discovered by Schaudinn and Hoffmann in 1905, is an extremely minute spiral or corkscrew-shaped filament, visible under only the highest powers of the microscope, which increase the area of the object looked at hundreds of thousands of times, and sometimes more than a million of times. Even under such intense magnifications, it can be seen only with great difficulty, since it is colorless in life, and it is hard to color or stain it with dyes. Its spiral form and faint staining have led to its being called the _Spirochaeta pallida_.[4] It is best seen by the use of a special device, called a dark-field illuminator, which shows the germ, like a floating particle in a sunbeam, as a brilliant white spiral against a black background, floating and moving in the secretions taken from the sore in which it is found. Some means of showing the germ should be in the hands of every physician, hospital, or dispensary which makes a claim to recognize and treat syphilis. [3] See frontispiece. [4] Pronounced spi-ro-kee'-ta.