Diaphragm

(dif-af-ram). I. The wall, muscular at the circumference and tendinous at the center, that separates the thorax and abdomen. The chief muscle of respiration and expulsion. 2. A thin septum, such as is used in dialysis. 3. In microscopy, an apparatus placed between the mirror and object to regulate the amount of light that is to pa through the object. D., Central Stop, in microscopy, a diaphragm having a circular slit just within its margin, the center remaining opaque. D. Iris, a device for changing or regulating the amount of light directed upon an object under the microscope. D. Opening. The opening in the disc or apparatus of a microscope through which the rays of light pa . It should be of about the same size as that of the front lens of the objective.