class="fnanchor pginternal" tag="{http://www.w3.org/1999/xhtml}a">[6] is the earliest sign of reaction which the body makes to the presence of the growing germs of syphilis. This always develops at the point where the germs entered the body. The incubation period ends with the appearance of a small hard knot or lump under the skin, which may remain relatively insignificant in some cases and in others grow to a considerable size. Primary lesions show the greatest variety in their appearance and degree of development. If the base of the knot widens and flattens so that it feels and looks like a button under the skin, and the top rubs off, leaving an exposed raw surface, we may have the typical hard chancre, easily recognized by the experienced physician, and perhaps even by the layman as well. On the other hand, no such typical lesion may develop. The chancre may be small and hidden in some out-of-the-way fold or cleft, and because it is apt to be painless, escape recognition entirely. In women the opportunity for concealment of a primary sore itself is especially good, since it may occur inside the vagina or on the neck of the womb. In men it may even occur inside the canal through which the urine passes (urethra). The name "sore" is deceptive and often misleads laymen, since there may be no actual sore—merely a pinhead-sized pimple, a hard place, or a slight chafe. The development of a syphilitic infection can also be completely concealed by the occurrence of some other infection in the same place at the same time, as in the case of a mixed infection with syphilis and soft ulcers or chancroids. Even a cold-sore on the mouth or genitals may become the seat of a syphilitic infection which will be misunderstood or escape notice.