1. The confusion sometimes found in discussions of dietary vitamin A and its precursors is illustrated. The relative potency of vitamin A and carotene is briefly discussed, and the procedure used in the National Food Survey of Great Britain explained. 2. Changes in the vitamin A and carotene contents of the British diet over the last two decades are illustrated. 3. The vitamin A and carotene contents of the American diet are estimated, and compared with those of the British diets; both estimates of intake are compared with recommended allowances. The difficulties of making such comparisons are discussed, in view of the different conventions used in the two countries. 4. An appendix, on the calculation of vitamin A in the diet, is included, in which interrelations between different methods of expressing vitamin A value are shown.

1. Subcutaneous fat thickness has been measured by three different techniques in forty-one subjects. 2. Ultrasound provided the most accurate measurement in experienced hands. 3. A method based on electrical conductivity was also accurate but was unpleasant for the subject. 4. Harpenden calipers were the least satisfactory of the three techniques tested.

1. Methionine-deficient diets were given to rats for 4 weeks. 2. This resulted in a decrease in total body iron, due to a decrease either in Fe absorption or Fe retention. 3. There was inhibition of growth, development of anaemia and a shift of body Fe to the liver. 4. There were no histological alterations which could be interpreted as specific to methionine deficiency. 5. These findings were different from reports of effects of ethionine in which there is an increased Fe absorption and various tissue alterations, including pancreatic acinar and liver damage.

1. In ileal contents from differently fed ruminating calves, examined under conditions approximating to those obtaining in vivo, 34–74% of the magnesium and 63–93% of the calcium were non-ultrafilterable. The binding was shown to be due to at least two processes, one depending on the presence of phosphate, the other not. 2. Considerable non-phosphate binding occurred in samples adjusted in vitro to pH 5.5 and above. The binding material was probably not a single substance but the bound forms of both Mg and Ca were, at least partly, in equilibrium with the soluble forms, and some competition between the two metals occurred. Thus in any one sample the extent of binding for either metal was influenced by the concentration of both. With normal concentrations it was estimated that, in the ileum, about one-third of the Mg and half of the Ca was bound in this way, irrespective of whether pasture or one of a variety of stall diets was given. 3. Samples adjusted to about pH 6.5 and above (in vivo ileum pH was about 7.4–7.9) showed further precipitation of Ca and Mg to an extent which partly depended on the concentration of inorganic phosphate. Ca precipitation appeared to be mainly controlled by the concentration of Ca and inorganic phosphate but for Mg the precipitation depended also on the presence of factors other than Mg and inorganic phosphate. One such factor found to be present was the ammonium ion, but its practical importance is uncertain. 4. Ileal contents from milk-fed calves showed considerable non-phosphate binding of Ca but not of Mg.

1. Assessment of sugar intake by our short questionnaire has been shown to agree well with its assessment by the conventional method in which subjects keep a 7-day diary of their diets. 2. People who have had a myocardial infarct, or are suffering from peripheral vascular disease, tend to reduce their intake of sugar. We believe this is the reason why investigators making dietary studies several months, or years, after infarction have not found the relatively high sugar consumption in patients with infarction that we had reported earlier. 3. The most suitable method for ascertaining dietary intake depends both on the constituent or constituents to be examined, and on the purpose of the investigation.

1. Portions of a preparation of freeze-dried cod fillet were subjected to different conditions of heat treatment and were then digested in vitro with pronase (an enzyme preparation from Streptomyces griseus), or successively with pepsin, pancreatin and erepsin, or with pepsin and papain. The digestions were conducted under ‘static’ conditions in flasks, and also in Sephadex gel G 10 in such a manner that the reaction products were continuously removed from the site of action of the digesting enzymes. The different digests were then passed in turn through a calibrated column of Sephadex gel G25 and each was resolved into three fractions containing ‘soluble protein’, ‘peptide’ and ‘free amino acids’. The distribution of several amino acids in these different fractions was determined and the results were assessed in relation to the availabilities of these amino acids in the original test proteins as measured in microbiological and chemical tests and, in some instances, in growth tests with rats. 2. The different enzyme systems gave broadly similar results. With increasing severity of heating, the ‘ free amino acids’ component in the digests became increasingly deficient in several amino acids relative to their content in the original unheated meal, and notably in lysine and the sulphur-containing amino acids. This evidence for a marked differential effect of heating in retarding the enzymic release in vitro of several amino acids was consistent with the results of feeding tests with rats, and of microbiological and chemical assays, which showed corresponding differences in the proportions of lysine, methionine and isoleucine made unavailable by the heat treatment. In severely heated meal more of the lysine, methionine and isoleucine was released by enzymes in vitro than was biologically available to the rat. With increasing severity of heat treatment, the biological availabilities of these amino acids for the rat fell more sharply than did the digestibility of the nitrogen, indicating that amino acids absorbed from the heated meals were relatively poorly retained.

1. Rats were maintained from the age of 3 weeks until the end of a second reproductive cycle on diets having different protein values and Ca concentrations. 2. Reproductive performance was judged from the number of viable young, their size, body composition and rate of growth during suckling. 3. The size and quality of the bones of the mothers and offspring were assessed from radiographs, histological appearance, total weight of ash, ash/cm3 and ash:organic matter ratios of dry fat-free bone. 4. At the end of gestation the mean numbers and total weights of foetuses were low when the mothers had received diets of low protein value: there were smaller differences in the body-weight, water, ash and N contents of the individual foetuses. 5. When 0.44% Ca was included in the diet of low protein value, only one (three rats) of the six litters born survived beyond 1 week of age. 6. At weaning, the young born of and suckled by the protein-calorie deficient dams were only about half the weight of those from mothers receiving the high-protein diets; Ca deficiency produced relatively minor changes. 7. All the mothers lost weight during lactation irrespective of the protein value or Ca concentration of the diet; their bones had lower radiographic densities and less ash/cm3 than is usual in non-pregnant rats of similar age. 8. The interaction of protein and Ca and their relative importance in maintaining the skeletal structure of mother and offspring during pregnancy and lactation are discussed.

1. A total of sixty-three wether lambs, 4–6 months old, were fed on diets low in phosphorus and adequate in calcium (0.072–0.073% P, 0.38–0.40% Ca) or adequate in both (0.38–0.40% P, 0.40% Ca) for 134 or 142 days. 2. Concentrations of serum inorganic P and Ca and alkaline phosphatase activity were studied during the depletion period. Bones were taken for histological analysis at the end of the 142 days. 3. After the preliminary depletion period, a metabolism study was conducted in which the effects of previous P depletion and dietary Ca:P ratio upon Ca and P absorption, as measured by isotope techniques, were studied. 4. Histological analysis of bones showed the presence of lesions characteristic of late rickets in some sheep and of severe osteoporosis in others. 5. A wide dietary Ca:P ratio had no apparent effect on P absorption when P intake was adequate. The availability of P was lowered by a diet deficient in P with a wide Ca:P ratio. 6. Previous P depletion resulted in enhanced P absorption during the first 11.5 days after an increased intake of P, but this effect was not shown during days 14–21 after the increase. 7. Ca absorption was reduced by giving a diet low in P and was increased when the intake of P was raised. 8. The response to wide dietary Ca:P ratios by ruminants and non-ruminants is reviewed, and a hypothesis, based upon a knowledge of the intestinal reaction of these species, is offered for the finding that ruminants tolerate wider dietary Ca:P ratios than non-ruminant species.

1. A combination of balance and isotope techniques was used to determine the influence of phosphorus depletion on the size of the exchangeable calcium pool and on the rates of Ca deposition in and removal from the whole skeleton of sheep. 2. The exchangeable Ca pool was reduced in size in the depleted sheep to approximately 50% of that in the controls. 3. The rates of Ca deposition in and removal from bone were reduced by P depletion and the rate of Ca transfer from the pool was reduced slightly. 4. The turnover rates of the exchangeable Ca pool and bone Ca in sheep appear to be similar to values published for man.

1. The nutrient content and distribution of the carcass meat in broilers (B) and free range cockerels (FR) was studied in two experiments in 1961–2. Half the birds of each type were roasted at 177°C, without additional fat, before dissection and analysis. The breast muscles and red meat were separately analysed for moisture, protein, fat and thiamine. 2. Chunky hybrids (frozen) and Light Sussex × Rhode Island Red (LS × RIR) cockerels were used in both experiments. Expt 1 (group 1) was a pilot study (using groups of six) inwhich B and FR of similar dressed weight were compared. Expt 2 (group 2) consisted of twelve ‘fresh’ (B1) and twelve frozen (B2) broiler hybrids from the same batch of birds killed at 9 weeks; twelve slightly heavier LS × RIR cockerels (FR2) were killed at 18 weeks and twelve Sykes hybrid 3 cockerels (FR1) killed at 20 weeks. The birds received various standard feeds. 3. The edible portion (skin plus meat), expressed as a percentage of the dressed weight, was greater in the free range birds than in the broiler chickens. Increased cooking losses resulting from freezing were responsible for a significantly smaller proportion of edible meat in the cooked frozen broilers. In both groups the edible portion increased with age irrespective of breed or weight. 4. In broiler and free range chickens differenccs in the mean protein content of the total edible meat were small. 5. Fat content appeared to be related to breed as well as to type of bird. In group 1, B contained slightly more fat than FR1. In group 2, B1, and B2, contained significantly more fat then FR1, but the fat content of the raw meat in FR2, was greater. 6. In both experiments the flesh of the free range chickens contained more thiamine than the broiler meat. In group 1 this difference was significant in all the cooked birds; in group 2 significant differences between free range chickens and broilers were found in the breast and red meat of the cooked birds for all comparisons except FR2 and B1. About one-third of the thiamine was lost on cooking both types of chicken in group 1; in group 2 the loss from the broilers was similar but in the FR birds between 18% (FR1) and 26% (FR2) of the thiamine was destroyed. 7. In general the meat of the broilers contained less thiamine and more fat than did that of the free range chickens. Though such differences are of no significance in a mixed diet (as chicken supplies so little thiamine) they are a useful index of differences in nutritive value which result from the different systems of management.

1. A gas-liquid chromatographic method for the detection of phytosterols in tissues and excreta of birds was developed. The limitations of this method are discussed. 2. β- and γ-Sitosterol werc detected in the plasma of adult cockerels and in the plasma, intestinal wall, and liver of 4-week-old cockerels. The proportion of sitosterols in the total sterol absorbed appeared to be affected by the nature of the dietary fat. 3. γ-Sitosterol was more effectively absorbed than β-sitosterol. The ratio of β to γ was altered by the nature of the dietary fat. 4. Using a diet containing 10% triolein and 1% cholic acid, and increasing the dietary plant sterol level up to 2%, increased the proportion of sitosterols in the intestinal wall of 4-week-old cocks. Further increases in dietary plant sterols did not produce additional increases in the proportion of sitosterols among intestinal wall sterols. 5. γ-Sitosterol and traces of β-sitosterol were found in eggs from hens given a diet supplemented with maize stcrols.

1. The Chorleywood Bread Process is a new method of making bread in which the 2–4 h of bulk fermentation of the dough normal in breadmaking is replaced by a few minutes of intense mechanical agitation to a controlled degree in special high-speed mixers. It is now being used to make over 30% of British bread. 2. Bread was made in a commercial bakery from two white flours by the Chorleywood Bread Process and a conventional method. 3. Both the bread and flours were analysed for moisture, protein, ash, fat, carbohydrate (by difference), thiamine, nicotinic acid and ascorbic acid. 4. More bread was made by the two processes from two other flours in a pilot-scale bakery. These breads and flours were used to determine net protein utilization values. 5. It was concluded that bread made by the Chorleywood Process cannot be distinguished from conventional bread in its content of protein, fat, ash and nicotinic acid, and in protein quality as indicated by its net protein utilization value. This was true for two grades of flour. In these tests the contents of thiamine and moisture were slightly higher and of carbohydrate slightly lower in Chorleywood than in conventional bread. No ascorbic or dehydroascorbic acid could be detected in any of the bread.

1. A machine is described which automatically releases previously weighed rations to individually penned sheep at hourly intervals for 24 h. 2. Six sheep were kept in a room with constant light, temperature and continuous background noise and given 912 g lucerne daily at 10.00 h or at hourly intervals by means of the automatic feeder. Faeces and urine were collected every 2 h. 3. Hourly feedings reduced the variation between 2-hourly collection periods by 47, 87, 90, 85, 70 and 91% for total dry-matter content of the faeces, faeces dry-matter concentration, total urine output, urine specific gravity, urine nitrogen concentration and total N content of the urine respectively.

1. Injections of 32P and 45Ca were used to study the influence of phosphorus depletion and repletion on the rates of endogenous calcium and P excretion in fifteen P-depleted and eighteen control sheep. 2. When given adequate P, there was a marked increase in the rate of excretion of metabolic faecal P in sheep which previously had been depleted. In control sheep a decrease was found in metabolic faecal P excretion with a diet deficient in P. 3. From the values for metabolic faecal P an indirect estimate of total intestinal secretion was made. The estimate was found to be in approximate agreement with values derived from published values for total daily digestive secretions in sheep. 4. The estimated rates of secretion of intestinal P suggest that after the addition of P to the diet the changes in the rate of excretion of metabolic faecal P in P-depleted sheep were the result of a decreased reabsorption of intestinally secreted P rather than of a change in the rate of secretion into the intestine. After a diet low in this element the decrease in metabolic faecal P excretion by control sheep appeared to be the result of a decreased rate of intestinal P secretion. 5. The possible significance of changes in metabolic faecal P excretion in relation to body P homoeostasis in the ruminant animal is discussed.

1. Sheep fitted with rumen cannulas were fed at hourly intervals by an automatic feeder in a controlled environment and the contents of the reticulo-rumen were removed at intervals of 6 h, 30 min after the previous feed. 2. No diurnal variation was found in the total contents or in the quantity of dry matter, organic matter and nitrogen. 3. Nine dried pasture herbages containing 0.79–3.69% N in dry matter were given automatically at a high and a low level of feeding. Feeding at the high level increased the total weight of the reticulo-rumen contents, total dry matter, organic matter and N and also the dry-matter percentage. 4. Apparent retention times were calculated by dividing the quantity of organic matter or N in the rumen by the quantity given each hour. Organic matter was retained for 10.2–24.9 h and N for 12.0–61.4 h. 5. The apparent retention times for both organic matter and N were reduced when the level of feeding was raised.

1. Two sheep were given cubed rations in which the fatty acid content was increased by about 12 g/day at the end of each week, until the daily intake became 74 g. 2. The apparent digestibility of the crude lipid increased with the increased intake, but there was no tendency for the digestibility of the fatty acids to increase or decrease regularly. 3. Comparison of faecal losses during the final periods, when a maximum amount of lipid was given, with the losses during the initial control periods showed that the excretion of dry matter, crude lipid and cellulose increased. The excretion of crude protein was unchanged and that of lipid- and cellulose-free dry matter decreased. There was a reduction in the production of methane of 17 kcal/100 kcal of additional fatty acids in the diet. 4. The concentration of the C18 unsaturated acids in the rumen liquor reached a maximum during the 1st week on the diet containing the maximum amount of added fatty acids. The shape of the curves was consistent with rapid hydrogenation of linolenic acid. The concentration of stearic acid in the rumen liquor reached a maximum when the dietary acids increased to only 50% of their maximum value.

1. Susceptibility to dietary induction of hypercholesterolaemia and aortic atherosis was compared in two groups of male New Zealand White rabbits. 2. Twelve rabbits were purchased from one breeding establishment (group I) and twelve from another (group 2). On arrival at the laboratory six animals from each group were killed and the aortas were removed. Blood samples were taken from the remaining twelve animals and then they were given ad lib. for a period of 40 weeks an atherogenic diet containing 20% butterfat. During this period food intake and body-weight were recorded. At the end of the period blood samples were taken from the animals and immediately afterwards they were killed and the aortas were removed. 3. No atheromatous lesions were found in the aortas of the rabbits in either group killed at the beginning of the experiment. There were no differences between the two groups of animals with respect to body-weight or concentration of cholesterol in the plasma at the beginning of the experiment, food intake during the experiment or body-weight at the end of the experiment. At the end of the experiment, the degree of aortic atherosis in the rabbits of group I was considerably greater than that in the rabbits of group 2. 4. At the end of the experiment the concentrations of total lipids, free cholesterol, esterified cholesterol and phospholipids in the plasma of the rabbits in group 1 were significantly higher than the corresponding concentrations of these lipid components in the plasma of the rabbits in group 2. The concentrations of palmitic, stearic and linoleic acids in the cholesterol esters and the concentration of palmitic acid in the unesterified fatty acids in the plasma of the rabbits in group 2 were significantly higher than the corresponding concentrations of these fatty acids in the plasma cholesterol esters and unesterified fatty acids in the rabbits of group 1. 5. It is concluded that these differences in response to the atherogenic diet were reflections of the differences in the susceptibilities to the dietary induction of hypercholesterolaemia and atherosis of the two differents strain of rabbit that had been established by the two commercial breeders. Such differences in susceptibility could readily explain certain discrepancies in the results of various research workers engaged in this field of investigation.

1. The relationship of vitamin A and carotenoids with encephalomalacia was examined in chick-raising farms and under laboratory conditions. 2. In encephalomalacic chicks on the farms a significant decrease in liver carotenoid content was demonstrated. In the diseased chicks the carotenoid contentwas below 0.30 mg/100 g liver, as against the normal values of 0.40–1.0 mg/ 100 g. 3. Under experimental conditions incidence of encephalomalacia could be decreased by oral treatment with the synthetic carotenoid ethyl β-apo-8'-carotenoate. This implies that deficiency in carotenoid is not merely a concomitant sign of encephalomalacia, but has also a causative role, as sufficient carotenoid reserves confer a certain protection against the disease. 4. The pathogenetic role of carotenoid metabolism in encephalomalacia was supported by certain observations. Factors inhibiting the accumulation of ethyl β-apo-8'-carotenoate in the liver predispose chicks to the disease. In chicks 4–5 weeks old in addition to those with vitamin A reserves higher than 800 i.u./g liver, the accumulation of carotenoids in the liver was about 10% of that measured in chicks more than 7 weeks old, or in those with vitamin A reserves not higher than from 100 to 200 i.u./g. In fact, encephalomalacia occurs mainly among chicks 3–5 weeks old. Also, reserves of vitamin A exceeding 800 i.u./g liver were found to predispose chickens to encephalomalacia.