DDT residues in the soil of an extensive salt marsh on the south shore of Long Island averaged more than 13 pounds per acre (15 kilograms per hectare); the maximum was 32 pounds per acre (36 kilograms per hectare). A systematic sampling of various organisms from the vicinity showed concentrations of DDT increasing with trophic level through more than three orders of magnitude from 0.04 part per million in plankton to 75 parts per million in a ring-billed gull. Highest concentrations occurred in scavenging and carnivorous fish and birds, although birds had 10 to 100 times more than fish. These concentrations approach those in animals dying from DDT poisoning, which suggests that many natural populations in this area are now being affected, possibly limited, by DDT residues. Similar concentrations have been reported elsewhere in North America.

SUMMARY Ischaemic colitis due to non-occlusive mesenteric ischaemia is a disease of the elderly which commonly involves the left side of the colon; selective splenic flexure involvement is said to be especially common. In an attempt to explain these features postmortem angiograms were performed on the superior and inferior mesenteric arteries of 37 postmortem subjects. A distinct agerelated tortuosity of the long colic arteries was noted which could account for the increasing incidence of ischaemic colitis with age. No anatomical basis for the higher incidence of left-sided involvement was found and, specifically, no critical point in the arterial circulation at the splenic flexure was demonstrated.Ischaemic colitis is a term introduced by Marston in 1966 to describe all degrees of ischaemic injury of the colon ranging from superficial mucosal necrosis to full-thickness infarction. Ischaemia of the colon may follow occlusion of the large or small vessels which supply that organ but in many cases of ischaemic colitis there is no demonstrable blood vessel occlusion (Renton, 1972). These cases of nonocclusive mesenteric ischaemia are thought to be caused by low flow states in the splanchnic circulation, often following a hypotensive episode (Renton, 1972;Aldrete et al., 1977). Characteristically, this type of intestinal ischaemia occurs in older, often debilitated, patients, many of whom have chronic cardiac disease and may be taking digitalis preparations. The left side of the colon is said to be more frequently involved in ischaemic colitis and the splenic flexure is regarded as being the area most at risk (Marcuson, 1972; British Medical Journal, 1977).Hypotensive episodes, while undoubtedly more common in older patients, are not the prerogative of the elderly, yet intestinal ischaemia following a hypotensive event is extremely rare in young patients, only four such cases having been described in the literature (Carey et al., 1967;Renton, 1967;Rickert et al., 1973;Turnbull and Isaacson, 1977).Using postmortem angiographs we have studied the anatomy of the colonic circulation over a wide 'Address for reprints: P. Isaacson, Department of Pathology, Southampton General Hospital, Southampton S09 4XY. Received for publication 1 December 1977 age range in an attempt to explain this discrepancy and to account for the reports of the high incidence of splenic flexure and left-sided involvement. The study showed that a distinctive age-related change occurs in the entire colonic circulation which could account for the age distribution of ischaemic colitis. The concept of a critical point or 'watershed' area in the circulation at the splenic flexure was not supported and we could find no anatomical reason for a greater incidence of left-sided disease. MethodsThirty-seven subjects were selected from routine hospital necropsies to include a wide age range (new-born to 92 years). There were 18 females and 19 males. Complete evisceration of internal organs was performed with division of the rectum as low as possible and the...

Intestinal suction biopsies were obtained in 15 infants and children with cutaneous colo-ureterostomies. The patients were subdivided into groups according to the length of time the conduit had been established, i.e. less than 5 years, 5 to 10 years, 10 to 15 years and over 15 years. The histological changes found were chronic inflammation with a dense infiltration of plasma cells and eosinophils. The changes were progressive and correlated with the length of time the conduit had been established. As persistent chronic inflammation is a precursor of malignancy, it seems likely that there is a risk of malignant change in these conduits. Regular follow-up of such patients is recommended and should include flexible fibreoptic endoscopy of the conduit.

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