People are always confused of where to apply the saliva. Many sellers do not even use the microscope and I hey know nothing about the usage. The saliva should be applied to the slide as in the attached video. Once you pull out the lens, it will come out with the slide, exposing the green light emitting diode. Never screw the lens out. Screwing in and out is for zooming and this only necessary when you are analysing the result for clearer vision of the result.