_Spirochæte pallida_ is most easily demonstrated in chancres and mucous patches, although the skin lesions--papules, pustules, roseolous areas--often contain large numbers. Tissue-juice from the deeper portions of the lesions is the most favorable material for examination, because the organisms are commonly more abundant than upon ulcerated surfaces and are rarely accompanied by other micro-organisms. After cleansing the surface a superficial incision with a scalpel or sharp needle is made at the edge of a lesion, or the surface is gently scraped away with a curet, and a drop of blood and serum is expressed. The less blood the better, because the {283} corpuscles may hide the spirochæte. Very thin cover-glass smears are then made. Goldhorn's stain gives very good results. It can be purchased ready prepared from E. Leitz, New York. The unfixed smear is covered with the stain for four or five seconds. The excess of stain is poured off, and the preparation introduced _slowly, with the film side down_, into distilled water. It is held in this position for four or five seconds, and is then washed by shaking about in the water. By this method the _Spirochæte pallida_ appears of a violet color, which can be changed to bluish black by flooding with Gram's iodin solution for fifteen or twenty seconds. The preparation is then washed, dried, and mounted. SEMEN Absence of spermatozoa is a more common cause of sterility than is generally recognized. In some cases they are present, but lose their motility immediately after ejaculation. Semen must be kept warm until examined. When it must be transported any considerable distance, the method suggested by Boston is convenient. The fresh semen is placed in a small bottle to the neck of which a string is attached. This is then suspended from a button on the trousers so that the bottle rests against the skin of the inguinal region. It may be carried in this way for hours. When ready to examine, place a small quantity upon a warmed slide and apply a cover. The spermatozoa are readily seen with a one-sixth objective (Fig. 53). Normally, they are abundant and in active motion. Detection of semen in stains upon clothing, etc., is {284} often important. The finding of spermatozoa, after soaking the stain for an hour in normal salt solution or dilute alcohol and teasing in the same fluid, is absolute proof that the stain in question is semen, although it is not possible to distinguish human semen from that of the lower animals in this way. [Illustration: FIG. 131.--Seminal crystals (medium size) (X750) from a stain on clothing. A single thread one-eighth inch long was used in the test, the stain being three years and four months old (Peterson and Haines).]