smear. All body discharges contain extraneous materials, such as pus cells and mucus. Of interest, however, are the types of bacteria that may be present. The stained smear reveals only two features: the morphology and the staining characteristics of the bacteria present. Positive identification requires cultures and further studies. Hospital Corpsmen should report only what they see. For example, “Smear shows numerous gram-negative bacilli.” If two or more types of bacteria are seen in a smear, the rule is to report them in order of predominance. For example: “1. Numerous gram-positive cocci in clusters 2. Few gram-negative bacilli” Gram-positive organisms are easy to see because they stain a deep blue or blue-black. Gram-negative organisms stain a deep pink, but since the background material is also pink, minute and detailed inspection is necessary before reporting the results. In the presence of gonorrhea, the smear will reveal large numbers of pus cells with varying numbers of intracellular and extracellular gram-negative, bean-shaped cocci in pairs. Such a finding could be considered diagnostic. It is important to point out that only a few of the thousands of pus cells on the slide may contain bacteria, and sometimes it requires considerable search to find one. SEROLOGY LEARNING OBJECTIVE: Recall principles and procedures for the Rapid Plasma Reagin (RPR) Card Test and the Monosticon DRI-DOT® Slide Test. Serology consists of procedures by which antigens and reacting serum globulin antibodies may be measured qualitatively and quantitatively. Serologic tests have been devised to detect either antigens present or antibodies produced in a number of conditions. Most tests are based on agglutination reactions between an antigen and a specific antibody. An antigen is a substance that, when introduced into an individual who does not already possess that substance, may stimulate the individual’s cells to produce specific antibodies that react to this substance in a detectable way. The five basic characteristics of an antigen are that it must be foreign to the body, it must possess a high molecular weight, it must be structurally stable, it must be complex, and it must have a high specificity to stimulate tissues to produce a defensive protein substance called an antibody. Antibodies are the specific defensive proteins produced when an antigen stimulates individual cells. Antibodies are produced by the host in response to the presence of an antigen and are capable of reacting with antigens in some detectable way. The antigen-antibody reaction takes place when a reaction occurs between specific antibodies in the plasma and the antigen present on cell surfaces. Principles and procedures of two serologic tests, the rapid plasma reagin (RPR) card test and the Monosticon DRI-DOT® Slide Test are covered in the following sections. RAPID PLASMA REAGIN (RPR) CARD TEST The RPR Card test is a sensitive, easily performed screening test for syphilis. The test is performed on unheated plasma or serum. Everything needed for the test is in a kit that is available commercially. This test kit is very useful aboard ship and at small stations. Principle of the RPR Card Test In the RPR Card test method of syphilis detection, a specific antigen (carbon-particle cardiolipin) detects “reagin,” a substance present in the serum of persons who are infected with syphilis. Specimens that contain reagin cause formation of particles (called flocculation) or coagulation of the carbon particles to occur on the RPR Card antigen. Reactive specimens appear as black clumps against a white background. Nonreactive specimens appear as an even, light-gray color. Materials Required for RPR Test To perform an RPR Card test, the following materials are required:  Serum sample—venous blood collected in tubes without anticoagulant. NOTE: Use clear, unhemolyzed serum that has been separated from the blood cells as soon after collection as possible.  RPR Card Test Kit, which consists of the following components: —RPR Card antigen suspension 7-29