1. The acute toxicity of orally administered CCl4 and its subacute toxicity (liver necrosis and hepatic fat accumulation) were studied in young adult male and female rats. CCl4 was more toxic in males than in females. The protective effects of vitamin E (D-α-tocopheryl acetate) and three synthetic antioxidants, DPPD (N,N'-diphenyl-p-phenylenediamine), ethoxyquin (6-ethoxy-1,2-dihydro-2,2,4-trimethylquinoline) and BHT (butylated hydroxytoluene) were studied.

2. Three daily oral doses (450 mg/kg) of vitamin E given before CCl4 increased survival in male rats but not consistently in females. Single oral doses (450 mg/kg) given previously at times between 24 and 72 h were also protective in males, but slightly decreased survival in females. Single intraperitoneal doses (500 mg/kg) given to female rats 1–48 h before CCl4 had no effect on survival. None of these treatments with vitamin E significantly decreased CC14-induced hepatic triglyceride accumulation. A large oral dose (2000 mg/kg) 6 h before CCl4 not only significantly increased hepatic fat accumulation but also increased mortality.

3. Three daily doses (600 mg/kg) of DPPD or a single oral dose given 72 h before CCl4 increased survival in male and female rats. When single doses of DPPD were given 6–48 h before CCl4 they had no effect on survival. In contrast, DPPD usually significantly decreased the CC14-induced hepatic triglyceride rise when given orally 6–72 h before CCl4. Single intra-peritoneal doses (100–1500 mg/kg) of DPPD, given 1–48 h before CCl4, decreased the hepatic triglyceride rise. Multiple doses of DPPD decreased CC14-induced liver necrosis, but single doses were generally less effective.

4. Three daily oral doses (300–500 mg/kg) of ethoxyquin given before CCl4 were highly effective in preventing mortality, liver necrosis and the rise in hepatic triglycerides. Single oral doses (500 mg/kg) given 72 or 48 h before CCl4 produced the same effect, but these single doses 24 or 6 h before CCl4 were without effect. The effective treatments usually increased liver weight markedly. Intraperitoneal treatment with ethoxyquin also substantially reduced the toxicity of CC14. Ethoxyquin was the most effective of all four treatments studied, and livers from animals given this substance were often nearly normal in histological appearance.

5. The activity of oral doses (400–600 mg/kg) of BHT, given 48 h or more before CCl4 was, in general, similar to that of ethoxyquin, but less marked. This substance also caused a large increase in liver weight after 48 h. Oral doses given 6–24 h before CC14 increased the CC14-induced triglyceride rise still further. Intraperitoneal doses of BHT were ineffective against acute toxicity, liver necrosis or the triglyceride rise.

6. Concentrations of a-tocopherol and the three synthetic antioxidants were measured in liver in many of the experiments. Very high hepatic concentrations of a-tocopherol could be obtained without affecting either the acute or subacute toxicity of CCl4. Ethoxyquin and BHT were rapidly eliminated from the liver after oral dosage, and when maximum concentrations were reached (24 h or less after administration) they were without protective effect. In contrast, when ethoxyquin and BHT were most active (48–96 h after administration) they could not be found in appreciable concentration in the liver.

1. The efficiency of production and utilization of vitamin B12 was studied with sheep given a cobalt-deficient diet with and without supplementary Co (1 mg/d). Vitamin B12 to lignin ratios in rumen contents were used to estimate minimum rates of production and these were related to faecal and urinary excretion. Tissue distribution and excretion of vitamin B12 were studied with [58Co]cyanocobalamin and 5′-deoxyadenosyl[60Co]cobalamin.

2. Labelled Co was rapidly sequestered by particulate material in the rumen and was largely excreted in the faeces. Most of the vitamin B12 in whole rumen contents was contained in micro-organisms, but was released on incubation at pH 2. Added cyanocobalamin was partly degraded in the rumen.

3. The vitamin B12 to lignin ratio in rumen contents began to decline 1–3 d after cessation of a daily Co drench. Estimated ruminal production of vitamin B12 on full feed was not less than 400–700 μg/d with supplementary Co and 50–110 μg/d from the Co (0.01–0.05 μg/g dry weight) in the basal diet. Production of vitamin B12 appeared to be limited by food intake with or without additional Co.

4. At full feed the efficiency of production of vitamin B12 from Co in the basal diet was about 13% while that from added Co was about 3%. Part of the vitamin B12 produced in the rumen was degraded before reaching the faeces and about 5% was absorbed. The minimum total requirements of sheep for vitamin B12 are assessed at about 11 μg/d.

5. Injected 5′-deoxyadenosylcobalamin was better retained than injected cyanocobalamin, faecal excretion exceeded urinary excretion with both. Labelled cobalamin was selectively retained by liver (particularly by the mitochondria), kidneys and the walls of parts of the alimentary tract. Vitamin B12 was secreted into the duodenum and reabsorbed in the ileum, but little secretion occurred above the duodenum and little absorption below the small intestine.

1. The fasting metabolism of twenty-seven animals, nine Brahmans, nine Africanders and nine Hereford × Shorthorns was measured after fasts of 96 h duration. Urine was collected over successive 24 h intervals and gas exchange was determined 96–103 h after the last meal.

2. Urinary urea decreased and creatinine increased throughout the fasting period. There was no difference between breeds in the urinary excretion of nitrogen, urea and creatinine on the 4th day of fasting (72–96 h). Excretion of nitrogen, urea and creatinine increased by 259, 197 and 45 mg/kg increase in fasted weight and by 8.9, 7.6 and 0.91 mg/kcal increase in fasting metabolism respectively. Protein oxidation accounted for 25.6, 21.7 and 22.7% of the fasting heat production of Brahman, Africander and Hereford × Shorthorn cattle respectively, values which were not significantly different.

3. The breeds differed in fasting metabolism per kg fasted weight ( P < 0.05) and in fasting metabolism adjusted for fasted weight (0.05 < P < 0.10), mainly owing to lower values for the Brahmans. The respective values for the Brahmans, Africanders and Hereford × Short-horns were 20.7, 25.2 and 24.1 kcal/kg (86.6, 105.4 and 100.8 kJ/kg) and 5.856, 6.947 and 6.600 Mca1/24 h (24.50, 29.07 and 27.61 MJ/24 h) at a fasted weight of 277 kg. The variation in fasting metabolism between animals within breeds, expressed as a coefficient of variation, was 13.7%.

4. The results are discussed in relation to published estimates of fasting metabolism, possible reasons for the breed difference and the relation of fasting metabolism to heat tolerance.

1. Studies were made with pair-fed vitamin B12-deficient and vitamin B12-treated or cobalt-treated ewes fed a Co-deficient diet in cages. Measurements were made of body-weight changes and some observations were made of energy and nitrogen metabolism. The effects of oral Co on energy and nitrogen metabolism were examined in sheep fed the Co-deficient diet, but not yet deficient of vitamin B12 in the tissues.

2. The rate of loss of body-weight of vitamin B12-deficient sheep was significantly faster (P<0.01) than that of pair-fed sheep given 50 μg vitamin B12/d by injection.

3. In a limited number of observations of pair-fed sheep no significant differences were found in retention of combustible energy from the diet, but excretion of faecal nitrogen was higher in deficient animals than in animals receiving vitamin B12 or Co.

4. There was no significant effect of supplementary Co on energy metabolism, nitrogen metabolism, production of methane or digestibility of fodder in sheep that were not deficient of vitamin B12.

1. A study was done on the platelet 5-hydroxytryptamine (5HT) from Africans in areas where endomyocardial fibrosis is common.

2. There were only small differences between the mean platelet or blood 5HT in Europeans and plantain-eating Africans; the distribution of the results showed a wider scatter in the African community, including values outside the upper limits of normal but not within the range reported for carcinoid.

3. Patients in hospital had lower platelet 5HT contents regardless of cardiac condition or disease than healthy Africans on similar diets, suggesting no specific abnormality related to platelet 5HT levels and endomyocardial fibrosis.

4. A small number of radioactive studies suggested that only 1–4 % of oral 5HT may reach the platelets; a significant increase in platelet 5HT did occur after a plantain meal; the in-crease after a meal but not after oral 5HT may be explained by release of endogenous 5HT from the small intestine under the influence of the high bulk of the diet. Attention is drawn to the high incidence of adult intussusception and volvulus associated with such diets.

1. Copper deficiency was induced in newly hatched chicks by feeding on a milk-based diet for 12 d; effects of supplementation with ascorbic acid were studied.

2. Cu deficiency alone resulted in 30% mortality from aortic rupture. This was associated with a 20% increase in total acid mucopolysaccharides in the aorta, manifested as an increase in chondroitin sulphate and a relative decrease in hyaluronic acid. Cytochrome oxidase activity of liver and heart was less than half that of the controls.

3. Supplementing the Cu-deficient diet with 0.5 % L-ascorbic acid increased mortality to 40%, raised total aortic acid mucopolysaccharides to a higher level, and increased liver iron by 36%.

4. Supplementing the control diet with ascorbic acid decreased liver Cu by 30% and significantly reduced total aortic acid mucopolysaccharides.

5. The enhancement of the Cu-deficiency effect by ascorbic acid probably results from interactions between ascorbic acid and absorption or metabolism of Cu; untoward effects of supplementing the control diet with ascorbic acid may be interpreted as manifestations of ascorbic acid toxicity per se.

1. An examination has been made of the plasma amino acids of adult Uganda Africans at risk to endomyocardial fibrosis compared with people from areas where the disorder is rare. The amino acid profile, both free and in the protein of the main staples, has also been examined.

2. Plasma tryptophan was found to be low in adults at risk and intermediate in Africans receiving a higher protein intake, as compared with Europeans whose protein intake might include more than 40 % as animal products.

3. Leucine and valine were also low in the plasma of adult Africans at risk.

4. The non-essential amino acids alanine and glycine were increased in the adult Africans at risk.

5. The similarity of these changes with the changes seen in kwashiorkor by other workers suggests that adherence to limited vegetable diets may introduce a chronic stress with regard to certain essential amino acids.

6. Studies on the vegetable staples used by Africans established that they are particularly poor in tryptophan and such Africans are probably dependent on other sources for their trypto-phan. None of the staples was a rich source of leucine. Plantain contained relatively large amounts of histidine, and cassava of arginine.

7. A comparative study of muscle protein suggests that the composition is similar regardless of diet and species. Leucine is quantitatively one of the most important amino acids in the muscle profile.

8.The above findings are discussed in the context of the requirements for heart muscle and the high incidence of cardiomyopathies within such African communities.

1. The effects of varying levels of physical activity were tested in rats, starting at ages of 21, 32 and 55 days and continuing until go, 100, 125 and 205 days.

2. Weight changes did not differ significantly between the exercise groups, except in the groups tested up to 205 days, when both the exercised group and the group with limited activity were significantly lighter than the control group.

3. The weight of the soleus muscle was significantly greater in the exercised rats compared with controls and rats with limited activity, except in the oldest age-group. The weight of the tibialis anticus muscle did not differ significantly between the different exercise regimes.

4. Heart weight was not significantly affected by the exercise regime, except that in rats studied from 55 to 125 days; the group with limited activity had significantly lighter hearts than those in the control group or the exercised group.

5. The percentage body fat was lower in the exercised group compared with the limited activity group, and was less than the control group in both the rats studied up to 205 days and those studied from 21 to 90 days.

6. Isoprenaline produced less cardiac damage in the exercised rats than in controls or in rats with limited activity. Animals who died following injection of isoprenaline had a higher percentage body fat than those animals with minimal cardiac damage.

1. Feeding on a raw soya-bean diet (RSD) increased the levels of trypsin, chymotrypsin and pancreatopeptidase E but decreased the level of amylase in the pancreas of chicks as compared to a heated soya-bean diet (HSD), while supplementation of HSD with soya-bean trypsin inhibitors increased the activity of all four enzymes. HSD + trypsin inhibitors caused significant enlargement of the pancreas but only a slight depression in growth rate.

2. Fasting for 24 h of chicks previously given RSD and HSD increased the activity of all four enzymes but the increase was much greater in chicks previously given RSD than in those previously given HSD.

3. Feeding RSD for 4 d to chicks previously adapted to HSD resulted in a dramatic inhibition in growth rate, a small increase in pancreas weight, and an increase in the activity of all proteolytic enzymes, while no change in the amylase was detectable.

4. Trypsin, chymotrypsin and pancreatopeptidase E activities were assayed in the contents of the small intestine and caecum of chicks fed on RSD or HSD over a period of 35 d. Trypsin and chymotrypsin activities in the small intestine were lower in chicks fed on RSD while pancreatopeptidase E activity was almost equal or even higher in RSD-fed chicks, especially at the age of 35 d. Trypsin activity in the caecum of RSD-fed chicks was lower at all stages of the experiment, while the pancreatopeptidase E and chymotrypsin activities in the caecum of RSD-fed chicks exceeded the levels in the HSD group at the age of 21 and 35 d respectively. It would appear therefore that pancreatopeptidase E may play an important part in overcoming the inhibition of the proteolytic activity in the intestine of chicks fed on RSD.

1. Rats fed on a vitamin B12-deficient or -supplemented diet were given either neomycin or a mixture of streptomycin and erythromycin by mouth for between 7 and 15 d. The urinary excretion of methylmalonic acid and the levels of vitamin B12 in plasma and tissues and of acetic and propionic acids in caecal contents were measured.

2. Both treatments caused prompt reduction of methylmalonate excretion in the deficient rats. This was apparently due to depression of the production of some precursor of methyl-malonic acid, probably propionate, rather than to an immediate effect on vitamin B12 nutrition.

3. After withdrawal of the antibiotics, neomycin-treated vitamin B12-deficient rats appeared to become partly repleted in vitamin B12, but the change in the vitamin B12 status of those which had received streptomycin and erythromycin was much smaller.

1. Metabolism of urea in non-pregnant and pregnant sheep (1–25 d from term) has been examined. Injections of [14C]urea were used to estimate urea entry rate, urea pool size and urea space in sheep given 1000 g of a diet of equal parts of crushed oats and chaffed lucerne hay (day a) and in the same sheep 4 d after the ration had been reduced to 250 g (day b).

2. On both experimental days (a and b), mean pool size was greater (14% on day α, 29% on day b) and urea space was greater (54% on day α, 24% on day b) in pregnant animals than in non-pregnant animals; mean plasma urea concentrations were lower (35%) in the pregnant animals on day a but were not significantly different on day b.

3. The entry rate of urea was similar in all the animals on day a, but was significantly higher (34%) in pregnant than in non-pregnant animals on day b. There was a significant decrease in urea entry rate in both pregnant (33%) and non-pregnant (86%) animals on day b.

4. The rate of excretion of urea was lower (26% on day a, 35% on day b) in pregnant animals, indicating a higher (31% on day α, 40% on day b) rate of degradation of urea in the digestive tract of pregnant as compared with non-pregnant sheep.

5. Measurements of urea entry rate have been used to calculate the upper limit of amino acid deamination in pregnant and non-pregnant sheep, and this has been used as an indication of the potential availability of amino acid carbon for glucose synthesis. It is suggested that, at a maximum, amino acids may have contributed the carbon required for 63 g/d and 52 g/d of glucose on days a and b respectively.

1. The mean liver retinol reserve (retinal + retinyl esters, expressed as retinol) of six newborn lambs was 21±8 μg. The mean value for ten suckled lambs, aged 5–7 days, was 2655±472 μg retinol per liver.

2. Three unsuckled lambs were fed ad lib. from birth for 28 days on a high-protein diet, based on lard and skim milk, without supplementary vitamin A. The diet provided sufficient vitamin A for normal growth, but insufficient to permit substantial liver reserves (43±8 μg retinol per liver).

3. Thirty-six suckled lambs aged 5–7 days were given either a low-or a high-protein diet for 21 days, with or without graded levels of retinyl acetate or βcarotene. There were no significant differences in the live-weight gain or in liver retinol reserves between the low-and highprotein dietary treatments, or between the supplemented and unsupplemented groups.

4. Twelve lambs were pair-fed on either a low-or a high-protein diet from birth for 21 days. Six lambs that were given a large supplement of retinyl palmitate on the 1st day of life had stored significantly less retinol in the liver at 21 days (P > 0.01) than six lambs given a somewhat smaller total amount of retinyl palmitate in small daily doses. Lambs given the high-protein diet had significantly greater liver retinol reserves (P > 0.01) than lambs given the low-protein diet, with both methods of supplementation.

5. Twelve lambs were pair-fed from birth on a high-protein diet for 2 or 6 days. Lambs that were given retinyl palmitate dissolved in either a low-or a high-protein diet on the 1st day of life had significantly lower liver retinol reserves some 24 h later (P > 0.01) than lambs given similar treatments on the 5th day of life. Liver retinol reserves were positively correlated with the protein concentration of the diet at the time of supplementation.

6. Eighteen lambs were pair-fed from birth with either a low- or a high-protein diet. Six pairs were given retinyl palmitate daily and three pairs were given the supplement 48 h before slaughter. The source of protein was casein. Eight out of nine lambs given the low-protein diet would have died had they not been slaughtered at between 8 and 11 days of age. The time of supplementation had no significant effect on liver retinol reserves, which were very low, regardless of the dietary protein concentration. Lambs given the high-protein diet retained a significantly greater proportion (P > 0.05) of the dietary retinyl palmitate than lambs given the low-protein diet.

1. Sheep confined topens and given a cobalt-deficient ration which supplied about 30μgCo/d required for maintenance of normal growth rate a Co supplement approaching 40 μg administered per os daily; for maintenance of what appeared, under the conditions of the experiments described, to be the maximum vitamin B12 status of a sheep, namely 3 ng vitamin B12/ml serum and 1.4 μg vitamin B12/g liver tissue, a supplement of between 0.5 and 1.0 mg Co/d per os was necessary.

2. For maintenance of normal growth rate the minimum daily requirement for vitamin B12 of sheep given the Co-deficient diet was about 11μg: about 5 μg absorbed from the gut and about 6 μg injected parenterally.

3. Extrapolation of the linear regression obtained by plotting the amount of vitamin B12injected/d against concentration of vitamin B12 in the liver tissue of a sheep indicated that to attain a concentration of 1.4 μg vitamin B12/g liver (wet weight) injection of 34 μg vitamin B12/d was necessary.

4. Comparison of the relative effects on body-weight of the administration of 100 μg vitamin B12/dper os and 3.12 μg vitamin B12/d by injection to sheep given the Co-deficient diet indicated that the efficiency of absorption of the vitamin from the gut was < 3%.

5. Loss of appetite, the first symptom of vitamin B12 deficiency to appear in the sheep, occurred when the concentration of vitamin B12 in the liver was reduced to about 0.1 μg/g wet weight.

6. In sheep given a supplement of 1 mg Co/d per os neither production in the rumen nor absorption from the gut but rather capacity for storage limited the concentration of vitamin B12 in the liver.

7. Following treatment to restore the vitamin B12 status of a sheep whose stores of the vitamin had been depleted, there was a linear negative correlation between the increase in the concentration of vitamin B12 in the liver and the concentration prior to treatment.

8. Following withdrawal of treatment from a sheep whose stores of vitamin B12 were adequate, there was a linear positive correlation between the rate of depletion of vitamin B12 from the liver and the concentration prior to cessation of treatment.

9. The concentrations of vitamin B12 in the serums of sheep given the Co-deficient diet, and given a supplement of 1 mg Co/d per os 0.5 h after feeding, remained relatively stable over the period 0–7 h after feeding; maximum concentration occurred 7–8 h after feeding.

10. Under the conditions of the experiments described a significant linear regression existed between concentration of vitamin B12 in the liver of a sheep and the logarithm of the concentration in the serum.