Biodegradable Mg implants offer advantages over permanent implants such as stainless steel that are used for broken bone repair. Mg alloys gradually dissolve, avoiding the need for removal by a later surgery if complications arise. Here we report a visual H sensor that can be used in the research laboratory to monitor the corrosion process in vivo during animal testing of different Mg alloys. The sensor consists of a plastic sheet with a thin coating that changes color in the presence of H gas. The sensor is easily used by taping it on the skin over the Mg implant. The color change gives a map of the H level permeating from the degrading Mg through the skin above it. This low cost, simple method of monitoring the dissolution of biodegradable implants would greatly facilitate the development of the biodegradable materials, especially in animal studies where in vivo biodegradation is tested.

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What's in a Name?One standard procedure for testing mental status is to present an object to a patient for visual, tactile, auditory, or even olfactory recognition and pose the question, "What is this?" Disordered naming (anomia) is a major indication of higher cortical dysfunction, and confrontation naming is a straightforward, valuable screening test. The procedure, however, yields minimal information about the processing of higher level information. Recognition and identification of an object and the presentation ofan appropriate name or symbol for the object demand action by much of the brain.The report by Caselli and associates in this issue of the Proceedings (pages 783 to 791) illustrates the complex nature of simple naming. Their 60-year-old patient had suffered a brain abnormality, probably herpes encephalitis, 6 years earlier; both magnetic resonance imaging and single photon emission computed tomography demonstrated a left temporal abnormality that involved particularly the anterior and medial aspects. Clinical evaluation with a series of specially devised tests demonstrated that their patient was unable to name presented objects or to point to the object when the name was presented, a bidirectional disturbance of semantic information. The authors also demonstrated that a similar naming disorder existed for tactile and auditory stimuli. In contrast, their patient was able to repeat the names ofthe objects when they were spoken by the examiner and to read names aloud. The authors interpret this ability to verbalize from spoken or written stimulus as evidence of competent lexical knowledge. In some, but not all, instances, their patient could demonstrate the proper use of an object that could not be named, but she could not (as many patients with anomia can) describe the use ofan Address reprint requests to Dr.