By the use of trypan blue, i.e. lipoid insoluble acid stain, in order to make observation of absorption activity of the oral mucosa, animals' mucosa with rapid absorption activity, its location, absorbing process, and absorbing conditions were investigated. Then clinical and biological observation on absorption of hormone of the salivary gland was tried. Ⅰ. Mixture containing equal parts of 1 per cent solution of trypan blue and saturated sodium bicarbonate solution was dropped and painted over the normal oral mucosa of various kinds of animals, such as dog, cat, hamster, albino rat, chicken, elaphis virgatus, lizard, rana esculenta, eft, and crusian and absorption of the solution was observed. The results obtained were as follows: 1) Absorption varied according to the kinds of animals. 2) In general absorption of the lower verbetrata was more remarkable than that of mammals and birds. 3) In mammals that of dogs was more marked than that of cat, hamster and albino rat. 4) In dogs marked absorption was seen in buccal and sublingual mucosa, particularly at the sublingual and parotid salivary papillae and their surrounding areas. 5) In albino rats absorption was made at the hard palate corresponding to the tip of the tongue. Ⅱ. In premature dogs it was equal to that of mature dogs. Ⅲ. No absorption was seen in the oral mucosa of the dog's and rabbit's fetus, while slight one was seen around the erupted teeth of the guinea-pig's fetus. Ⅳ. T.B. was not introduced into the ep. cells of rabbit's oral mueosa in case of vital staining. Ⅴ. The effects of various factors on T.B. absorption of the oral mucosa in dogs' experiments were as follows: Absorption-stimulating factors are, local thermal stimulation, Grace helio lamp irradiation. roentgen irradiation of amount of 60 r to 100 r, radium irradiation of amount of 33 mg. h, to 66 mg. h., intracranial amputation of maxillary and mandibular divisions of trigeminal nerve just after the procedure. and local injection of Teabrom (T.E.A.B.), in the early stage of injection, while absorption-inhibiting factor was local cold stimulation and no absorption was stimulated in case of anemia of the head following ligation of the common carotid artery. Ⅵ. Parotin and Saliva-parotin, i.e. hormone of the salivary gland was painted over the oral mueosa of man, clog and rabbit. The results obtained were as follows: 1) Leucocytosis was noticed in cases of dog (1.2~5.0 mg./kg. of Parotin administered) and man (0.2~0.4 mg./kg. of Parotin or 0.1-0.2 mg./kg. of Saliva-parotin administered), 2) decrease of serum Ca. and leucocytosis in case of rabbit (1.0-5.0 mg./kg. of Parotin and Saliva-parotin administered), and 3) stimulated calcification of dentine in case of rabbit (5 mg./kg. of Parotin administered). These results Will suggest us the following factors as those effecting on absorbing mechanism of the oral mueosa, especially of the epithelium: 1) resistance, 2) intensity of surface tension, 3) intercellular density, 4) characteristics of chemical substances and solvent, and 5) special vital function of the cells.