An in vivo microscopic and ultrastructural study of tissues transferred to the transparent rabbit ear chamber is presented. Fragments of liver, kidney, thyroid, and myometrium were successfully auto- or allografted into the chamber from donors of all ages and allowed continuous in vivo observation of parenchymal structure and function, as well as of the graft vasculature which plays such an active role during rejection. Circulation was quickly reestablished by anastomosis of graft vessels to those of the ear chamber membrane and only minor reversible parenchymal changes occurred. Both vessels and parenchyma retained the characteristics of the organs of origin on both light and electron microscopy and were observed functioning in vivo for periods up to 1 yr in the case of autografts, and until rejection occurred in allografts. In the latter case, rejection did not occur in tissues obtained from adult and neonatal donors for nearly 3 months, while tissues of fetal origin were generally rejected much earlier. The kidney grafts provide a unique opportunity for a close comparative study of mammalian fetal and adult glomerular blood flow under varying rates of perfusion, and the tubular epithelium could be observed regenerating after initial acute tubular necrosis. Renal tubules from fetal, neonatal, and adult donors were all capable of metaplastic change to form a highly ciliated epithelium. Grafts of these tissues will allow the fine detail of the processes of rejection to be studied continuously in vivo.
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