[-Overexposed film--underexposed film-].

Physics of the radiographic exposition are presented, including those of the radiating image, contrast, sensitometry. Based on these principles, the modifications which allow correcting over- and underexposition of the images are explained.

[Practical value of the descending ray angle in the axial femoropatellar study. Sensitizing role of external rotation of the skeleton of the leg in the 30 degree F.P angle].

The descending ray, or so-called "inverted", axial femoropatellar view, used much less frequently than the classical ascending view, is described. This view is easy to perform, but requires very rigorous positioning of the patient and the equipment. All of the practical details are illustrated by photographs.

[Value of a new apparatus for percutaneous vertebral bone biopsy].

Percutaneous vertebral trephine biopsy is a valuable investigation. A new type of trephine needle for vertebral biopsy is described in this paper. This trephine needle is introduced on the thin needle used for local anesthesia, following a procedure similar to vascular catheterism.