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Caecal coccidiosis in chickens can be effectively treated with certain sulphonamides, particularly sulphamezathine (sulphadimethylpyrimidine) (Horton-Smith and Taylor, 1943) and sulphapyrazine . Sulphamezathine was extensively used in the treatment of outbreaks of caecal coccidiosis on poultry farms during the 1945 and 1946 seasons. On some of these farms a few chicks did not thrive during treatment and a small proportion died. The only apparent abnormality found on post-mortem examination of such chicks was the presence of haemorrhages of the intestines and occasionally of the liver and skeletal muscles. The appearance of such chicks resembled that described in vitamin K deficiency and the haemorrhagic form of sweet clover disease. In order to investigate this syndrome, sulphamezathine was dosed to chicks experimentally and way found to produce hypoprothrombinaemia in most chicks. Internal haemorrhages, similar to those found in the field, were observed in a small proportion of cases.In the course of these experiments cockerels dosed with sulphamezathine for periods longer than 10 days showed premature development of combs and wattles; such cockerels had enlarged testes with hypertrophy of the seminiferous tubules. A brief account of these effects has been published (Asplin, Boyland, and Horton-Smith, 1946). EXPERIMENTALExcept where otherwise stated Rhode Island Red (R.I.R.) chicks of mixed sexes or Light SussexxRhode Island Red cockerels were kept on dry standard mash or placed on experimental diets when one week old. The sulphonamides were administered as solutions of the sodium salts in the drinking water. In some experiments chicks were weighed at weekly intervals to determine the effect of treatment on body growth. Blood from recently killed chicks was taken by heart puncture and placed in tubes containing sodium oxalate. The plasma was separated by centrifugation and the prothrombin time determined by a modification of the method of Witts and Hobson (1940); the only change in the method was the omission of lecithin. The prothrombin times were determined on undiluted plasma

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