Abstract. Evaluation of mortality during a two-year period at a primate colony indicated that 34% of nonexperimental deaths in macaques one year of age and older were due to gastrointestinal disease. Of deaths related to gastrointestinal disease, 12% had acute gastric dilatation, 18% had shigellosis, 12% had nontuberculous mycobacterial disease, and 58% were of undetermined cause. Histologic evaluation of the alimentary tract indicated that the large intestine was the most common site of anatomical change in monkeys that had diarrhea at the time of death. Monkeys that had a single terminal episode of diarrhea had less gastric inflammatory lesions than those that had multiple episodes of diarrhea in the last year of life.Successful maintenance and breeding of nonhuman primates for biomedical research requires a healthy animal population. Gastrointestinal disease has been associated with 31% to 44% of the deaths reported in primate colonies [l, 31. In ongoing efforts to characterize and reduce spontaneous disease problems in macaques at the California Primate Research Center, a retrospective evaluation of naturally occurring enteric diseases was undertaken. These evaluations of deaths over a twoyear period were conducted to determine the incidence and causes of gastrointestinal disease and the associated histologic changes. Histologic evaluations were based on comparison with normal monkeys from the colony and included deaths with and without associated clinical signs of enteric disease. Materials and MethodsDuring the period of this study, monkeys were housed in both indoor and outdoor cages. Indoor cages were of various types including both group and individual caging. Outdoor caging consisted primarily of the corn-crib type (oval cages 5 m in diameter) maintained on a variety of surfaces including concrete, asphalt, gravel, and rock. The social grouping in outdoor cages was primarily of the harem type, although juvenile peer groups also were common. A more recent type of enclosure used by the Center is the field cage. These are 30x60 m and hold groups of 30 to 80 macaques. The animal management, feeding, and health surveillance have been described [4]. The average population of Macaca mulatta ranged from 1,100 to 1,250 and Macaca radiata from 290 to 350. During this time, 49% of the monkeys were wildcaught and 5 1% were colony-born. The colony averaged 34% males and 66% females.A complete necropsy was done on all monkeys that died or were killed at the Center,

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his paper presents the background and the results of T the first two years of a long-term field exposure of various types of plastic pipes in a gas-distribution system. The study is part of a program to establish the suitability of plastic pipes for gas-distribution uses. The work was initiated at Battelle in 1960 by the American Gas Association for the purpose of developing improved plastic pipe for gas-distribution service. It was soon apparent that, before an improved plastic pipe could be developed, the limitations of existing pipes had to be defined. The methods for defining these limitations ultimately became a major part of the program at Battelle. Information resulting from an earlier study at Battelle for the Thermoplastics Pipe Division, now the Plastic Pipe Institute of the Society of the Plastics Industry, Inc., indicated that the establishment of the long-term stress-rupture behavior with natural gas would be needed to demonstrate the potential use of plastic pipes for this application. This study became the major part of the laboratory work. Subsequently, however, it was deemed necessary to investigate other methods of evaluating plastic pipe that would be useful to the gas-distribution industry for detecting changes in mechanical properties. Thus, a considerable part of the program was involved in the development of test methods that could be used in defining those parameters of interest to the gas industry. A greater understanding of fatigue, permeability of the pipe, as well as resistance to impact, aging, and the effects of environments were some of the objectives of the laboratory work.Editor's Note: Actual tabular data used to construct graphs nre available from authors upon request. 111 the course of this work, the long-term stress-rupture tests with natural gas showed that the behavior with gas was essentially equal to that with water. The fatigue study showed that secondary stresses that might be encountered in the use of plastic pipe for gas distribution were not likely to be a serious factor in its long-term performance, provided the pipe was properly installed. The permeability studies demonstrated that none of the plastics currently used in the program would be expected to be eliminated as a potential material because of its permeability.About mid-1962, the activities of the A.G.A. Subcommittee on Plastic Pipe Standards revealed that several serious operational failures had occurred with plastic pipe in the gas-distribution industry. Most of these failures could be attributed to faulty installation but, in at least three serious failures, the plastics themselves appeared to be a factor. About this time, laboratory studies indicated that the fracture behavior of the pipes in the stress-rupture testing varied with both the stress-rupture life and temperature of the test. After available information on the three field-failure incidents was examined, it was concluded that the failures were aggravated by the presence of constituents other than methane in the gas. However, it was recognized t...