Mach bands, a visual phenomenon resulting from lateral inhibitory impulsess in the retina, are recognized aslucent or dense lines at the borders of different radiographic densities. A number of clinical situations have been described in which Mach bands may cause difficulty in radiographic diagnosis. Photodensitometric measurement of the film can differentiate the true change in film density from the Mach band which is an optical illusion. Authors present several examples of photodensitometric tracings of Mach bands, with the brief review of themechanism of their production.
Diagnosis ; Optical Illusions ; Retina

The issue of cold damage is one of the major topics of orthodox medicine in East Asia. From the historical view of point, most of the medical practitioners have turned The Theory of Cold Damage to account as their grounds for justifying their own argument. However, it is rare to find a book related to The Theory of Cold Damage in Korea's traditional medicine. Therefore, people have perceived the research status of cold damage is unsatisfactory. This problem could be analyzed by dividing it into a medicinal herb problems and theory problem. First, the medicinal herbs needed for the prescription based on The Theory of Cold Damage don't grow in the Korean Peninsula. Accordingly, there were a lot of restrictions on the free use of these prescriptions. Nevertheless, Chinese medicinal herbs were essential to even the use of the prescriptions besides The Theory of Cold Damage. Accordingly, such aspects do little explain the point that there were few medicine books about The Theory of Cold Damage in Korea. On the other hand, it is hard to exclude the guess that the medical practitioners in the period of the Joseon Dynasty might have presented a theoretically different opinion about cold damage. This study did intensive research on this. As a result of examining the medical practitioners in the latter period of the Joseon Dynasty perceived 'the cold damage to positive and negative meridians' as the case where a patient got attacked by cold as a pathogenic factor in a state of the kidney deficiency. They presented the verdict that kidney deficiency was mostly incurred by sexual relations, and the cold damage to positive and negative meridians broke out when a patient got attacked by cold as a pathogenic factor after having sex. it is an original standpoint shedding light on the relationship between cold damage and the kidney deficiency. The medical practitioners in the latter period of the Joseon Dynasty used Donguibogam as a major text for study on cold damage. In other words, Donguibogam includes the well-organized theory of Yeoksu school who regarded the comparison between internal damage and external damage as important. The medical practitioners in the latter period of the Joseon Dynasty managed to form the theory of the cold damage to positive and negative meridians by deepening the relationship between internal damage and external damage, which was highlighted in Donguibogam. The medical practitioners in the Joseon Dynasty didn't show a big interest in the literature itself, or the so-called The Theory of Cold Damage, which was mainly due to not only the realistic problem of the lack of medicinal herbs needed for applying the prescription to cold damage but also the difference between their positions on cold damage. Therefore, the idea of insufficient research on The Theory of Cold Damage is no more than a kind of optical illusion. On the contrary, we may assume that the medical practitioners in the Joseon Dynasty understood and developed The Theory of Cold Damage in their own way.
Asian Continental Ancestry Group ; Cold Temperature ; Far East ; Hand ; Humans ; Kidney ; Korea ; Light ; Medicine, Traditional ; Meridians ; Optical Illusions ; Plants, Medicinal ; Prescriptions