as a member of an anthropologic research team, you have occasion to visit a primitive tribe in the remote reaches of the Amazon jungle. During your visit, the natives conduct a ceremony celebrating the rites of passage for young males. This consists $,$ among other things, of veering their bodies with elaborate patterns of stripes and circles using a variety of colours extracted from local plants. On your return $3$ weeks later, you are asked to look at a young male who has developed alarmingly itchy and weepy red areas of skin that run in sharply demarcated stripes across his back and on one arm. Remembering your introductory course in immunology, you make an educated guess as to the cause. How, under such primitive conditions, could you confirm your diagnosis?