1. The question as to the absorbability of the bladder has not been answered satisfactorily but much mystery still surrounds its solution. Professor Tabayashi in this department has published numerous papers on the subject and the present investigation concerned, as a part of his general scheme, the absorption of silver nitrate solution from a histological point of view. The study endeavors to elucidate (1) the successive changes of the bladder tissue following the introduction of silver nitrate solution and the manner in which the silver is taken up by the tissue, and (2) the histological basis for explaining the rise and fall in the silver absorption curve as brought out by Dr. Oi. The literature contains a great deal of discussion whether silver nitrate solution is absorbed from the bladder at all, and, although the successful investigators admit its transportation into the tissue, the amount of of absorbed metal is exceedingly small. In his biochemical study Oi demonstrated that relatively large quantities of the solution could be absorbed by actually measuring the actual amount of the metal. However, the absorption curves this investigator obtained revealed frequent ups-and-downs in chronologically successive determinations which can not be explained by common knowledge of absorption. Oi merely attributes these facts by assuming the peculiar character of the solution as well as the specificity of the bladder mucus. These points are taken up in the present histological study.
2. For the purpose of these experiments the solutions of silver nitratet in various concentrations, such as 0.1% (1:1000), 0.133% (1:70) and 0.2% (1:500), were prepared, and 30cc of each were instilled into isolated bladders. Examination of the bladders was made from tissues removed at 8 regular intervals, namely, 15 and 30 minutes, 1, 2, 4, 6, 12 and 24 hours. Similar procedure was followed with intact bladders for control purposes. The tissue specimens were fixed in formalin, embedded in paraffin and stained by by hydroquinone, haematoxylineosin, as well as by Okamoto's silver method. All these staining methods are satisfactory for the purpose of the present study, since the silver reaction in the tissue is well brought out. The so-called formalin granules (pigments), which may be confused with silver, can be removed by treating the specimens in the Verocay's solution (alcohol+KOH).
3. The specimens so prepared all reveal the presence of silver in the superficial layer of the epithelium exhibiting degeneration and partial desquamation within 15 minutes. The silver infiltrates the deeper layer within 30 minutes, causing remarkable degenerative changes, although approximately 1 hour is required for almost complete desquamation. The desquamative change takes place not as a whole at once but piece by prece in successive steps. At the location of complete desquamation, the submucus tissue shows a naked exposure. This process is followed by the regeneration of the epithelium which requires 1-2 hours or more, and in the meantime the epithelium presents varied morphological changes consiting of epithelial buds, small immature form, large immature form and finally mature form. The immature form of the epithelium is capable of ingesting the silver solution and undergoes degeneration followed by desquamation. Thus the cycle of regeneration, silver ingestion, degeneration and desquamation proceeds in repetition.
The Submucous tissue is as a rule hypertrophic, while the propria, the muscularis and the serosa are hydropic and swollen in varying degrees. However, these findings show no further progress with the concentration of silver solution used in the present experiment. Vascular changes consist of the engorgement of capillaries beneath the submucus tissue and of portions of the venous ramification beneath the serosa, and some of these structures contain yellowish and dark brownish staining hues. These changes are already evident in specimens obtained

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