The box contains a small green bottle with anti-HCG serum (rabbit) and a red bottle with HCG latex suspension (antigen). A black glass slide with green rings serves as the working surface.
If the woman is pregnant, the anti-HCG serum’s antibodies are bound by the HCG in the urine. Latex particles coated with HCG, when added thereafter, cannot react with the antiserum. The latex solution remaining milky indicates a positive result.
If the woman is not pregnant, her urine will not contain HCG and the antiserum can react with the HCG-laden latex particles. This will result in agglutination (clumping), visible on the slide as granulation, which indicates a negative result.
Production stopped in the early 1980s.
Source: W. Pschyrembel, Praktische Geburtshilfe (‘Practical Obstetrics’), 1967