When the bacilli are scarce, the following method may be tried. It is applicable also to other fluids. If the fluid is not albuminous, add a little egg-albumen. Coagulate the albumen by gentle heat and centrifugalize. The bacilli will be carried down with the albumen. Separate the albumen, mix with artificial gastric juice (for preparation of which see test for pepsin, p. 222), and set in an incubator or warm place until digested. Finally, centrifugalize and stain as described above. The bacilli do not stain so well as in the ordinary methods. A careful search of many smears may be necessary to find the bacilli. They usually lie in clusters (see Plate V). Failure to find them in suspicious cases should be followed by inoculation of guinea-pigs; this is the court of last appeal, and must also be sometimes resorted to in order to exclude the smegma bacillus. * * * * * In gonorrhoea gonococci are sometimes found in the sediment, but more commonly in the "gonorrheal threads," or "floaters." In themselves, these threads are by no means diagnostic of gonorrhea. Detection of the gonococcus is described later (p. 264). [Illustration: PLATE V. Tubercle bacilli in urinary sediment; X800 (Ogden).] 7. Animal parasites are rare in the urine. Hooklets and scolices of _Tænia echinococcus_ (Fig. 55) and embryos of _Filaria sanguinis hominis_ have been met. In Africa the ova, and even adults, of _Distoma hæmatobium_ are common, accompanying "Egyptian hematuria." [Illustration: FIG. 55.--1, Scolex of tænia echinococcus, showing crown of hooklets; 2, scolex and detached hooklets (obj. one-sixth) (Boston).] [Illustration: FIG. 56.--Embryo of "vinegar eel" in urine, from contamination; length, 340 µ; width, 15 µ. An epithelial cell from bladder and three leukocytes are also shown (studied with Dr. J. A. Wilder).] Other parasites, most of which are described in Chapter VI, may be present from contaminations. A worm {129} which is especially interesting is _Anguillula aceti_, the "vinegar eel." This is generally present in the sediment of table vinegar, and may reach the urine through use of vinegar in vaginal douches, or through contamination of the bottle in which the urine is contained. It has been mistaken for _Strongyloides intestinalis_ and for _Filaria sanguinis hominis_. It closely resembles the former in {130} both adult and embryo stages. The young embryos have about the same length as filaria embryos, but are nearly twice as broad and the intestinal canal is easily seen (compare Figs. 56 and 107). C. EXTRANEOUS STRUCTURES The laboratory worker must familiarize himself with the microscopic appearance of the more common of the numerous structures which may be present from accidental contamination (Fig. 57).