1. Concentrations of the amino acids in the plasma of blood from the portal vein and hepatic vein and in the liver of fed rats and rats starved for 1 d or 3 d were measured. The 1 d values were compared with the equilibrium concentrations of the amino acids found in the perfusion medium during perfusion of livers from rats starved for 1 d.

2. The measurements of portal–venous differences in amino acid concentrations confirmed the idea that postprandially and during starvation most of the amino acids flow from extrahepatic tissues to the liver but also showed that during starvation tryptophan, cystine, ornithine, valine, leucinc and isoleucine flow in the opposite direction, from liver to extrahepatic tissues.

3. The blood levels of the non-essential amino acids fell markedly during starvation while those of the essential ones tended to be maintained. This contrasts with the pattern of changes known to take place in rats and man given low-protein diets. In the liver, changes in amino acid concentrations were generally related to those in the blood but not strictly parallel. The relative changes in amino acid concentrations in blood and liver indicate that as starvation progresses the concentrative ability of the liver is enhanced for most of the amino acids which are taken up and that the increased output of those which are released is also due to changed membrane transport.

4. The changes in plasma amino acid concentrations in the blood passing through livers of rats starved for 1 d were, except for tryptophan and perhaps cystine, consistent with the extracellular changes found during perfusion of livers form rats straved for 1 d, indicating that the perfused liver influences concentrations of extracellular amino acids substantially as it does in vivo.

5. The results suggest of mechanism wherby the liver may control the maintenance of the essential amino acids during starvation.

1. The reproducibility of an assay for methionine based on live-weight gains in young chicks has been tested in a collaborative study in six laboratories.

2. Results were analysed by the slope-ratio procedure and, in general, the assays were statistically valid. The variability between laboratories was similar to that found in previous studies of variablity within a single assay in one laboratory.

3. With the combined estimates from five or six laboratories the standard error of the estimates was apporoximately 10% of the mean. Expressing response as‘g gain/g food eaten’ gave no more precision than using ‘weight gain’ alone, but is nevertheless thought to be less open to error due to apetite effects.

4. The experiments have shown that materials can be ranked consistently, but that the absolute estimates of potency varied between assays and further improvements are desirable if potency estimates are to be used for the calibration of in vitro procedures of protein evaluation.

1. Measurements of the concentrations of amino acids in the plasma of blood from the portal vein and hepatic vein in the livers of rats made diabetic with streptozotocin or alloxan and starved for 1 d were compared with similar measurements from normal rats starved for 1 d.

2. The concentrations of many of the amino acids in the blood plasma were lower in the streptozotocin diabetic rats than in the normal animal while the liver concentrations tended to be increased. This suggests that there is enhanced concentration of these amino acids by the liver in diabetics, as is also found in starvation, which is probably due to factors other than the direct absence of insulin.

3. The direction of flow of the groups of amino acids into and out of the liver was unchanged in the diabetic compared with the normal rat except that the output of tryptophan was abolished, and that of the branched-chain group was abolished in alloxan diabetes though apparently enhanced in streptozotocin diabetes. The rates of movement of amino acids in both directions appeared to be increased in the streptozotocin diabetic animals.

4. The changed amino acid pattern in the alloxan diabetic rats was to some extent similar to that of the streptozotocin diabetic rats but the changes were more difficult to interpret, perhaps because of side-effects of alloxan on tissues including liver.

1. Yudkin's (1967) questionnaire on the dietary intake of sugar was given to 415 businessmen for self-administration.

1. The results showed an inverse relationship between sugar intake and relative weight (actual weight as a percentage of expected weight for height and age) and additional evidence suggests a direct relationship between sugar intake and adequate exercise.

2. The statement that ‘sugar was restricted’ was shown to be a factor of considerable importance affecting the reported level of sugar intake and should be taken into account when comparing different series.

3. The positive association between cigarette smoking and mean sugar consumption in this series was due to the low-sugar intake of ex-smokers.

4. In future studies on the role of sucrose in the aetiology of ischaemic disease, both smoking habits and levels of activity should be recorded.

1. Chicks and quail (Coturnix japonica) were used in the measurement of net protein utilization and true digestibility of nitrogen of isolated soya-bean protein and a mixture of casein and gelatin in zinc-deficient diets.

2. The net protein utilization values for both protein sources were increased when the diets were supplemented with Zn or with the disodium salt of ethylenediaminetetra-acetic acid, as was the true digestibility of nitrogen of the isolated soya-bean protein.

1. The colorimetric micro-adaption of the iodometric method and the colorimetric thiocyanate method for the determination of lipoperoxides were compared. Similar results were obtained when methyl linoleate hydroperoxide was tested, but when lipid from rat liver, muscle, kindney and testes was examined, substantial amounts were found by the iodometric, but almost nothing by the thiocyanate method.

2. The main reason for the discrepancy between the methods seems to be that the iodometric micromethod also estimates substances other than true lipoperoxides. The presence of ubiquinone and vitamin A in the organ extracts was shown to interfere in this way in the method.

3. The yellow colour which develops when retinol and its esters are tested by the iodometric micromethod is due not to liberated iodine but to conversion products of retinol.

4. It is concluded that the occurrence of substantial amounts of lipoperoxides in vivo has so far been demonstarted only in the adipose tissue, and not in the parenchymatous organs of the rat.

1. Monozygous twin cattle with permanent rumen fistulas were used to measure the rate of degradation of casein and ovalbumin. One twin was used as a control and the other had protein administered by fistula about 4.75 h after eating a standard ration.

2. Casein was rapidly degraded with a half-life in the range 5.6–21.5 min, with the formation of peptides, free amino acids and finally ammonia. Up to 43% of the casein nitrogen was found as ammonia in the rumen fluid. Most of the amino acids present in casein were found in the free state in the rumen fluid to an extent of less than 7%, but valine, leucine, isoleucine and lysine were present as 25, 27, 21 and 38% respectively of the amounts present in the casein administered.

3. When acid-hydrolysed casein was given, ammonia was rapidly formed, the maximum amount found in the rumen being equivalent to 39% of the casein N. The individual amino acids were rapidly broken down except for valine, leucine, isoleucine and lysine of which synthesis in addition to degradation may occur.

4. Ovalbumin was degraded slowly with a half-life of 175 min, which was reduced to 132 min by feeding the cattle with ovalbumin for 5 d. Ammonia was produced slowly.

5. When added together the two proteins were degraded in the rumen independently at their own rates.

6. δ-Amino-n-valeric acid was produced in large quantity when casein or casein hydrolysate was degraded in the rumen.

1. In the wild, red grouse live largely on heather, a high-fibre (25%), low-protein (7%) food. Digestibility trials were carried out under semi-natural conditions, with magnesium as a digestibility marker. Two trials were done, one in autumn and one in spring.

2. Digestibility of the dry matter varied from 21 to 30% and metabolizable energy from 1.1 to 1.6 kcal/g. These variations were inversely related to intake and could partly be accounted for by facultative variations in holocellulose and lignin digestion.

3. Digestion of soluble carbohydrates, protein (measured as α-amino-nitrogen) and holocellulose varied between trials according to the initial concentration in the food. The digestibility of soluble carbohydrate was high (78–83%) in autumn (16% in food) and low (61–66%) in spring (11% in food) and that of protein was relatively low (24–31%) in autumn (6% in food) and high (42–48%) in spring (7% in food). Digestibility of crude fat was 30–33% for four birds and 20% for one bird.

4. By comparison with poultry, voluntary intake of dry matter was very high relative to body-weight and intake of energy appeared to be adequate. None the less, all birds lost weight during the trials, presumably for reasons other than energy shortage.

5. Urate excretion increased in parallel with body-weight losses, but formed only 2% of the total N output at low weight losses, in which event the main nitrogenous compounds in the droppings were α-amino N (presumably largely from undigested protein), ammonium salts and ornithuric acid.

6. The ornithuric acid was presumably a detoxication product of prolignins and possibly tannins and other polyphenols. Its excretion by grouse corresponds to the excretion of hippuric acid by ruminants.

1. The amino acid incorporating activity of skeletal muscle ribosomes was studied in rats under various nutritional conditions using labelled amino acids.

2. Ribosomes were obtained from rats that were given a protein-free diet for 5 d followed by a high-protein diet containing casein, gelatin or wheat gluten for 16.5 h and from others that were given one of these protein-containing diets or one containing protein from polished rice for 6 d.

3. The level of isotope incorporation relative to RNA was somewhat higher when the protein source given for 16.5 h was a good-quality protein such as casein than with gelatin or wheat gluten, but fine discrimination between proteins was not considered to be feasible with this system.

4. In the rats that were given the protein-containing diets for 6 d the differences were more pronounced and the amino acid incorporating activity was correlated with the biological value of the protein.

1. Six experiments were undertaken with mature, dry, non-pregnant cows to determine the capacity to lose and recover nitrogen and to study the significance of the labile and total protein reserves.

2. It was concluded that, without altering its ability to reach N equilibrium, the mature cow is able to store and lose large amounts of body proteins (certainly more than 15 kg), when its N and energy intakes are greatly varied. The repletion or depletion of protein reserves can occur over a long period of time (sometimes more than 5 months). Total protein reserves include a very labile part. This part is more rapidly lost during fasting than during feeding on low-protein diets; it can be used to meet temporarily the energy requirements of the animal.

3. N balance and body-weight gains were generally very well correlated.

1. The amounts of available cystine and tyrosine in the protein of different animal tissues showed a close correlation with the level of hydroxyproline, and may be estimated from hydroxyproline values by regression equations.

2. Estimates of ‘chemical score’ have been calculated from the content of hydroxyproline determined in a series of samples for which net protein utilization (NPU) for rats had also been determined. Chemical scores calculated as percentages of the total ‘essential+semiessential’ amino acid content of each material correlated closely with NPU, whereas scores calculated as percentages of total amino acids did not. ‘Methionine+cystine’ were calculated to be first limiting amino acids in every sample.

1. In two experiments, sheep prepared with a rumen cannula and with re-entrant cannulas in the duodenum and ileum were continuously fed on diets of dried grass, dried grass plus formalin-treated casein, or dried grass plus untreated casein. Paper impregnated with chromic oxide was given once daily via the rumen fistula.

2. In ten 24 h collections of digesta entering the duodenum and eleven 24 h collections of digesta reaching the ileum of sheep given dried grass, there were highly significant correlations between the 24 h flows of Cr marker and the corresponding flows of dry matter, organic matter, nitrogen, gross energy, hemicellulose and cellulose (P < 0.01) at both sites.

3. Daily amounts of non-ammonia N and of individual amino acids entering and leaving the small intestine and of total N excreted in faeces and urine are given.

4. Net retention of supplementary N was 36% when the supplement was administered as formalin-treated casein, but only 17% when it was administered as untreated casein.

5. Formalin treatment of casein significantly increased the daily amounts of non-ammonia N entering the small intestine (P < 0.01) and the amounts of non-ammonia N apparently absorbed therein (P < 0.05).

6. Apparent absorption of amino acids from the small intestine was significantly greater (P < 0.05) with treated casein than with untreated casein. There were relative increases in the small amounts of several free amino acids measured, including taurine, in the ileal digesta of sheep receiving the treated casein supplement.

1. The intestinal absorption of [11,12 3H2] retinyl acetate was studied in five apparently normal children, eight children with respiratory infection and three with gastroenteritis.

2. The absorption of vitamin A was significantly lower in children with respiratory infection or gastroenteritis than in normal children.

3. In the light of these observations, it is suggested that repeated attacks of infections may significantly contribute to the prevalence of vitamin A deficiency in children of poor communities.

1. Sheep prepared with a rumen cannula and with re-entrant cannulas at the proximal duodenum and terminal ileum were given diets of dried grass, and dried grass supplemented with formalin-treated or untreated casein. They were fed either continuously or once daily. Paper impregnated with chromic oxide was given once daily via the rumen fistula.

2. The observed daily flows of magnesium at the duodenum and ileum were highly correlated with the corresponding flows of Cr.

3. There was a net absorption of Mg from the stomach as well as the intestinal region of all sheep.

4. Protein supplementation had no effect on the extent or sites of Mg absorption, but altering the feeding regimen changed the proportions of the net absorption of Mg occurring in the stomach and intestinal regions.

1. The body composition was determined of forty-one fetuses of different gestational ages born to mothers belonging to a low socio-economic group of the population.

2. With increasing gestational age the water content fell from 88% at 28 weeks to 76% at term; the fat content increased from 2.1% to 11.2% and the protein content increased from 6.9 to 9.3%.

3. The changes in body composition were more closely related to body-weight than to gestational age.

4. The calcium, Phosphorus and magnesium contents of the body per unit fat-free weight progressively increased with gestational age, and at term the values appeared to be considerably lower than those reported in the literature. The Ca:P ratio was constant at different body-weights.

5. The body iron content per unit of fat-free weight increased marginally with increasing gestational age. The value was almost 30% lower than the values reported from elsewhere.

6. It is suggested that chemical composition and nutrient stores of the developing foetus can be considerably influenced by the state of maternal nutrition.