The experiments were designed (1) to investigate the effects of various types of injury to the peritoneum on the formation of adhesions, and (2) to study the hitological changes of the intestinal wall when injured artificially with 5 % iodine tincture. The experimental animals used were Wistar adult male rats with a weight range of 90 to 120 grams. A total of 170 rats were used. Experiment 1. The experimental animals were divided into 10 groups, each group consisting of 10 to 20 rats. Group A. The caecal serosa was injured with 2 % iodine tincture. Group B. The caecal seroSa was injured with 5 % iodine tincture. Group C. The caecal serosa was abraded with gauze until subserosal petechies were produced. Additional trauma to this area waS inflicted with 2 % iodine tincture. Group D. The caecal serosa was injured as in group C, but 5 % iodine tincture was used. Group E. The caecal serosa waS injured with 2 % aqueous mercurochrome solution. Group F. The caecal serosa was rubbed with gauze until subserosaI petechies were produced. Additional trauma to this area was inflicted with 2 % aqueous mercurochrome solution. Group G. The caecal wall was rubbed with gauze 100 times, injuring the subserosa. Group R. The anterior wall of the stomach and caecum was traumatized with a toothbrush and 2 ml of aqueous talcum solution were instilled into the peritoneal cavity. Group I. Excisions of the parietal peritoneum were performed with a surgical knife over areas of varying sizes at both sides of the operation wound. Group J. Adjacent loop of the intestines with normal serosa were connected to one another by No.2 black silk suture at two or three points. In five cases of this group, contacting surfaces of the intestines were injured with 5 % iodine tincture. The results obtained were as follows : (1) Local administration of 2 % iodine tincture and 2 % aqueous mercurochrome solution would not produce adhesions unless mechanical injury, such as rubbing with gauze was also present. (2) When the serosa was slightly injured with gauze, fibrinous adhesions were separated or torn apart by bowel movements. (3) Local administration of 5 % iodine tincture produced in all members of group B. The adhesions were moderate, not extensive in degree. Additional mechanical trauma aggravated the adhesions caused by bacterial contamination. (4) Intraperitoneal instillation of 10 % aqueous talcum solution produced extensive adhesions. The favorite sites of occurrence of the adhesions were the greater omentum and the small intestine. (5) Excision of the parietal peritoneum over areas of vareous sizes caused no adhesion. (6) Even prolonged contact between the intestinal wall and normal serosa did not result in the formation of adhesions. However, firm adhesions resulted from prolonged contact between injured serosal surfaces regardless of the type of injury. (7) The author would like to emphasize that large peritoneal defects should be left untreated, because attempts at peritonealization result in additional injury to the subserosa and often in more extensive adhesions. Experiment 2. (1) Edema and an infiltration of leucocytes occurred in the early stages of the inflammation. These histological changes were seen not only in the subserosa, the muscular layer, and the submucosa, but also in the mucosa. Lesions in the mucosa slowly developed into necroses or ulcers. The intensity of the adhesions varied with the severity of the lesions in the mucosa. (2) Twenty-four hours after injury to the peritoneum, P. A. S. positive substances began to appear in the submucosa, disappearing fourth post-operative day. (3) The process of the formation of the adhesions may be outlined as follow: a) After injury to the peritoneal surface, an exudate is formed. b) Thise xudate coagulates to form fibrin, which causes adiacent surfaces to cohere. c) Dunng organization, fibroblasts or fibrocytes migrate into this area. e) Whth the aid of mucopolysacchrides in ground substances, collagen is deposited and grdually a firm adhesion is formed. In some cases, however, this area becomes membraneous or strand-like in form during the completion of the process of adhesions, and is eventually torn apart.