1. Changes in the serum amino acid ratio have been compared with alterations in liver composition in young rats growing on three different diets, control, low-protein and ‘undernourished’. The rate of growth in the latter group was controlled to be the same as in the low-protein animals.

2. The amino acid ratio only became elevated in the protein-deficient animals but not to the degree found in protein-malnourished children.

3. Protein/g DNA was lost from the livers of the protein-deficient rats and this occurred at the same time as the serum amino acid ratio rose. The possibility that the two phenomena might be linked is discussed. Protein loss from the liver was not a feature in the undernourished animals.

4. Reduced serum total protein and albumin concentrations also developed in the rats fed the low-protein diet and this occurred as the amino acid ratio started to rise.

5. The liver did not become fatty in the low-protein animals until after the amino acid ratio had reached its maximal value. It was concluded, therefore, that the distorted pattern of serum amino acids could not be a result of this pathological condition.

6. There was no apparent relationship between liver RNA levels and the magnitude of the serum amino acid ratio.

7. The limitations of the rat as animal model for the study of chronic protein malnutrition in early childhood are discussed.

1. One hundred and seven fine-wool Merino wethers and non-pregnant ewes varying in age from newly born to 110 months and in live weight from 1.7 to 55.1 kg were slaughtered and minced.

2. The nitrogen, fat, ash, calcium, phosphorus, sodium and potassium contents of the mince were determined. Energy content was estimated from the contents of fat and fat-free organic matter.

3. Weighted regression relationships were calculated between the energy, N, Ca, P, Na and K contents of the sheep, and age, live weight and (age x live weight). The relationships were differentiated with respect to age and live weight, and the rates of nutrient deposition at different rates of live-weight gain, and for sheep differing in age and live weight were calculated.

4. The rates of nutrient deposition were compared with those estimated by the Agricultural Research Council (1965) and by Mitchell (1962). and were in general lower in energy content and higher in ash constituents per unit live-weight gain.

1. Rats were given a rachitogenic diet for 28 days; some were dosed with vitamin D 2 or 3 days before they were killed and some received vitamin D throughout the experiment.

2. Parathyroid leucine aminopeptidase was measured histochemically as an index of parathyroid activity and silver impregnation as a criterion of bone calcification.

3. Calcium and phosphorus were estimated in bone ash and in serum. In rats killed 2 days after a single dose of vitamin D, increases were found in the Ca and P content of serum and bones and in epiphyseal Ca deposition. Parathyroid activity was decreased. In rats killed 3 days after a dose of vitamin D there was a marked increase in serum Ca and P but a less clear change in bone Ca and P although epiphyseal calcification was evident. The parathyroid activity was less than in rats dosed throughout the experiment.

1. [I-3H]Cholecalciferol and [I-3H]cholecalciferol palmitate in amounts equivalent to 2 μg cholecalciferol were injected into rachitic rats as aqueous preparations (intravenously) or in arachis oil (intramuscularly).

2. The radioactive faecal metabolites collected for up to 17 days were fractionated according to their polarity. The same pattern of excreted radioactivity was seen with intravenous and intramuscular cholecalciferol and intravenous cholecalciferol palmitate. Intramuscular chole-calciferol palmitate produced a higher proportion of the most polar metabolites in faeces.

3. Parenterally administered cholecalciferol palmitate in a rickets-healing biological assay had activity equivalent to unesterified cholecalciferol.

4. Vitamin D ester synthesized in vivo is considered to be eventually metabolized as vita- min D alcohol and to be available to vitamin D-requiring processes.

1. A dose of 1 g of riboflavine caused a large excretion of the vitamin in human urine and the rate of excretion showed more than one maximum.

2. Various degradation products of riboflavine appeared in the urine approximately 24 h after the dose was administered and two of these were identified as 7,8-dimethyl-10-(2-hydroxy-ethyl)isoalloxazine, and 7,8-dimethyl-10-formyl-methylisoalloxazine. Reasons are given for believing that the degradation of riboflavine was due to bacterial action in the colon.

1. In seven experiments sheep were given diets ranging from all-hay to all-barley, and also a diet comprising one part hay to two parts flaked maize. Each sheep was equipped with a cannula into the rumen and a re-entrant cannula in the proximal duodenum; six of the ten also had a re-entrant cannula in the terminal ileum. Paper impregnated with chromic oxide (Cr2O3) was given twice daily by rumen fistula.

2. Amounts of α-linked glucose polymer entering and leaving the small intestine and excreted in the faeces were measured. Some values for a fraction designated non-glucose reducing polymer for cellulose and for gross energy were also obtained. The amounts passing the proximal duodenum and the terminal ileum were adjusted to give 100% recovery of Cr2O3 and the values were used to measure the extent of digestion in various parts of the alimentary tract.

3. When rolled or whole barley was given alone or was the major feed constituent the amount of α-linked glucose polymer entering the small intestine was 6.0±0.76% of that ingested (range 2.6–8.1%). The value was significantly lower than that found for the diet of hay and flaked maize (10.4±1.3%, range 8.0–13.6 %).The α-linked glucose polymer which entered the small intestine was almost completely digested there.

4. The digestibility of the non-glucose reducing polymer, which included much of the hemicelluloses present, ranged from 51 to 73% and almost all the digestible fraction (93–97%) was digested before the small intestine when hay or predominantly hay diets were given. On high-cereal diets only 71–85% of the digested fraction disappeared before the small intestine and appreciable amounts were digested in the large intestine.

5. On the all-hay diet 91% of the digestible cellulose and 67% of the digestible energy were lost before the small intestine, 0 and 21% in the small intestine and 9 and 12% in the large intestine.

6. Mean digestibility coefficients determined in sheep fed solely on either whole or rolled barley were: for dry matter 88.1 and 87.9%, for nitrogen 83.5 and 82.1%, for crude fibre 53.7 and 56.6% and for gross energy 87.7 and 88.0%.

1. The fatty acid compositions of the plasma cholesteryl esters, phospholipids, triglycerides and unesterified fatty acids were determined in three sheep at various times after they had been given intra-abomasal infusions of emulsions of linseed oil, maize oil or linoleic acid.

2. The concentrations of linolenic acid or linoleic acid in the plasma triglycerides began to increase 1.5 h after infusion of the emulsions had begun. As the concentration of linolenic or linoleic acids in the plasma triglycerides increased, the concentrations of palmitic and stearic acids decreased, hut there were no appreciable changes in the concentrations of oleic acid.

3. The concentrations of linolenic or linoleic acid in the plasma phospholipids and cholesteryl esters did not begin to increase until 8–9 h and 24–25 h respectively after the infusions of the emulsions had begun.

4. It is suggested that, after absorption from the small intestine of the sheep, linolenic and linoleic acids are transported in triglyceride form to the liver where the triglycerides are partially or completely hydrolysed. These C18 polyunsaturated acids are then preferentially utilized for the synthesis of phospholipids and cholesteryl esters but not for the re-synthesis of triglycerides.

1. Groups of rabbits were given diets containing different proportions of butterfat and maize oil. After the animals had been given the experimental diets for 40 weeks the plasma phospho- lipids were fractionated and the fatty acid composition of each fraction was determined.

2. Phosphatidyl choline and lysophosphatidyl choline accounted for about 75 and 12% respectively of the total plasma phospholipids: phosphatidyl ethanolamine, sphingomyelin and phosphatidyl serine accounted for only about 5.3, 5.0 and 2.6% respectively. Changes in the linoleic acid content of the diet had little effect on the relative proportions of the individual plasma phospholipids, but there was an over-all decrease in the concentration of total phospholipids in the plasma as the linoleic acid content of the diet was increased from 0.25 to 10.6%.

3. When the diet contained 0.25 % linoleic acid, the linoleic acid:oleic acid ratio in the phosphatidyl choline (1.3) was similar to that in the phosphatidyl ethanolamine (1.2), but as the linoleic acid content of the diet was increased to 10.6% the linoleic acid:oleic acid ratio in the phosphatidyl choline increased to 48, whereas that in the phosphatidyl ethanolamine increased only to 2.2. Increases in the linoleic acid content of the diet resulted also in increases in the linoleic acid:oleic acid ratios in the phosphatidyl serine, lysophosphatidyl choline and sp hingomyelin.

4. When the linoleic acid content of the diet was increased, the stearic acid:palmitic acid ratio in the phosphatidyl choline increased, whereas it decreased in the phosphatidyl ethanol- amine and remained relatively unaltered in the phosphatidyl serine. The stearic acid contents of the lysophosphatidyl choline and sphingomyelin were unaltered by dietary treatments, but the palmitic acid content of these two phospholipids decreased as the linoleic acid content of the diet increased.

5. The results are discussed in terms of the metabolic relationships that exist between the various phospholipids.

1. Hooded rats were fed from weaning on a basal retinol-deficient diet containing retinoic acid. Such a diet maintains growth and general health but does not prevent the appearance of lesions associated with vitamin A deficiency in the retina and testis. Some animals were also given supplements of retinol averaging 0.1, 0.25, 1 or 5 μg retinyl acetate per day. Rats were killed at intervals up to 28 weeks after weaning. The weights of the testes and the histological appearance of the testes and epididymides indicated that 5 μg retinyl acetate per day had maintained spermatogenesis throughout the experimental period. Doses averaging 1 μg retinyl acetate per day were only partially effective and the two smaller doses had little beneficial effect.

2. In a second similar experiment rats were given doses of retinyl acetate averaging 0.25, 0.5, 1, 2 or 100 μg per day. Measurements of the electroretinogram thresholds of the rats indicated that a dose of 1 μg retinyl acetate per day maintained mainly normal vision until the end of the experiment 29 weeks after weaning. Additional histological observations made 21 weeks after weaning showed that this dose level had not maintained spermatogenesis but that doses of 2 μg retinyl acetate per day had been effective.

3. The experiments show that the differing functions of vitamin A in spermatogenesis and vision are reflected in the hooded rat in differences in the dietary retinol levels needed to maintain these processes.

1. An experiment was performed to study the effect of sodium acetoacetate on urinary excretion of santhurenic acid and other tryptophan metabolites in male albino rats.

2. Animals were fed on a nicotinic acid-deficient diet for a period of 3 weeks. The animals were then divided into two groups and, after the basal urinary excretion of the tryptophan metabolites had been estimated, the rats of both the groups were force-fed with L-tryptophan (100 mg per rat), the rats of the second group being simultaneously injected intraperitoncally with acetoacetate (200 mg/kg body-weight), and the urine samples during the following 24 h were collected and analysed.

3. Acetoacetate-treated rats given tryptophan were found to excrete significantly greater amounts of kynurenine, hydroxykynurenine and xanthurenic acid than the corresponding control rats. There was no ditference between the amounts of kynurenic acid excreted by the animals in the two groups.

1. The urinary excretions of total diethyl ether-soluble acids and total aromatic acids of three sheep given maintenance diets containing different proportions of hay, rolled oats and decorticated groundnut meal were determined.

2. When the sheep were given the diet containing 70% rolled oats the excretion of aromatic acids in the urine was less than that observed when the sheep were given diets high in roughage or protein concentrates.

3. The amounts of aromatic acids excreted in the urine were not related to the dietary intakes of crude protein, apparently digestible crude protein, crude fibre, lignin or cellulose.

4. The excretion of comparatively large amounts of aromatic acids in the urine of ruminants is discussed in relation to the smaller amounts normally excreted by non-ruminants. Possible reasons for the failure to observe any relationship between the amounts of aromatic acids excreted in the urine of the sheep and those constituents of the diets that were investigated are discussed and the nature of other precursors is suggested.

1. Fertile eggs deficient in vitamin A were obtained by feeding hens a diet deficient in retinol (vitamin A alcohol) but containing methyl retinoate.

2. Radioactive retinol was injected into the albumen of three of these eggs at a level of 2 μg [6,7-14C]retinol/egg. After 5 days' incubation, 4.6–8.3% of the injected material was recovered in the lipid of the embryo, representing a four- to nine-fold concentration into the embryo from the albumen. Approximately 40–50% of this was unchanged retinol, 15–20% retin-aldehyde and 20–30% probably a long-chain fatty acid retinyl ester. The early embryo can, therefore, metabolize vitamin A very effectively.

3. [6,7-14C]Retinoic acid (2 μg) was injected into normal fertile eggs, killing most of the embryos. The eggs with dead embryos were analysed; 0.24% and 0.33% of the injected material was recovered from the embryos. Two embryos which developed contained 0.51% and 0.53% of the injected dose. In no instance was any material identified other than retinoic acid. The extremely low amounts of retinoic acid absorbed by the embryos emphasize the very high toxicity of retinoic acid to the early chick embryo.

4. [6,7-14C]Methyl retinoate (0.5 μg) was injected into each of four normal eggs; 8.5–11.6% was isolated as unchanged methyl retinoate after 5 days; no other radioactive substance was detected.

1. Calcium balance studies were carried out on twenty-eight apparently normal preschool children who had been for several months on a low Ca intake of 200 mg/child per day.

2. Three-day balances showed that all subjects were in positive balance. The absorption was 50% of the intake.

3. When the dietary intake was increased to 280 mg/day there was a greater absorption and retention of Ca. Serum Ca, inorganic phosphorus and alkaline phosphatase were within the normal range for this age group.

4. Fourteen of the subjects were on wheat supplemented with lysine. The addition of a single amino acid to the diet was shown not to improve the absorption and retention of Ca over that of the controls.

1. Healthy young men ate diets high in carbohydrate with a fixed protein content: (a) 18% protein with maize starch, (b) 18% protein with sucrose, (c) 9% protein with sucrose. Sucrose or starch was given at a level of 7 g/kg body-weight per day.

2. The serum albumin concentration fell by 7–10% after 16 days with all three diets; the falls were statistically significant. No change in γ-globulin concentration was seen with the 18% protein diets. With the 9% protein diet there was a significant increase in this fraction. The β-globulin concentration rose significantly with the diet containing 18% protein with sucrose but there was no change in this fraction with the other diets. α1- and α2-globulins rose significantly with the diet containing 18% protein with sucrose but no increase in these fractions was seen on the other diets.

3. Possible mechanisms concerned in the production of these changes are discussed.

1. Artificial emulsions of nine synthetic triglycerides ranging from tripropionin to triolein were given as continuous infusions into the jugular vein of lactating cows for periods of 2 days. The effects of these infusions on the composition of blood lipids and on the secretion of the component fatty acids in milk were examined.

2. Tricaproin, tricaprylin, tripelargonin, tricaprin, trilaurin, trimyristin and triolein, in contrast to tripropionin and tributyrin, increased the yields in milk of the acid contained in the triglyceride. The increased yield of acid was positively correlated with chain length of the infused triglyceride, and with triglycerides above tricaprin the transfer of fatty acid to milk was sufficiently large to give consistently increased yields of total milk fat.

3. The infusions increased the concentrations in blood plasma of cholesterol, phospholipid and in some experiments also of triglyceride. Concentrations of these lipids returned to normal by 2 days after the infusion. The fatty acid compositions of the plasma triglycerides were not affected by the infusion of triglycerides up to tripelargonin but with triglycerides longer than this the plasma triglycerides were altered in composition towards that of the infused triglyceride.

4. Short- and intermediate-chain fatty acids of the infused triglycerides were elongated by the successive addition of two carbon units to give increased yields in milk of acids ranging up to C15 and C16 when they contained acids with an even and odd number of carbon atoms respectively. Possible interference with the conversion of stearic into oleic acid in the mammary gland owing to the infused emulsions is also discussed.

1. [24-14C]cholic acid was given orally to rats receiving three different diets, a semi-synthetic diet (D7) with and without 20% cellulose, and a commercial, pelleted diet. The labelled metabolites excreted in the faeces in the 8 days following administration of the labelled cholic acid were chromatographically separated, and tentatively identified by means of thin-layer chromatography.

2. In all three dietary groups the faecal bile acids mainly consisted of unconjugated and 7α-dehydroxylated metabolites. In rats receiving pellets or diet D7 with cellulcse, there was a higher percentage of monohydroxy-monoketo-cholanoic acids than in those receiving diet D7 alone. Dihydroxy-cholanoic acids, present in approximately the same ratio as were the 3α- and 3β-hydroxy isomers, were excreted by all the rats in the three dietary groups.

1. Two high-yielding varieties and three hybrids of pearl millet were evaluated for their chemical composition and protein efficiency ratio (PER) for rats at a level of 6.38% dietary protein. PER values ranged from 0.94 to 1.21 and were significantly different.

2. Tryptophan contents of the proteins were above the optimum level of the FAO reference protein. Lysine content was deficient in all the samples and was probably the limiting amino acid in the PER test.

1. The effects of dietary antibiotics (penicillin, neomycin or terramycin) on the absorption of D-glucose, D-galactose, L-arginine or L-histidine by the mouse were investigated by using sacs of entire everted ileum.

2. Compared with the controls, there was generally an increased absorption of all these solutes. Tissue uptake of the solutes remained unaltered. The inward movement of water into the sacs was increased but was generally independent of solute transport.

3. The body-weight decreased slightly and caecal weight increased with penicillin only. The weight of the small intestine decreased with the different antibiotics, and the gut wall became thinner. Faecal fat increased slightly, but not significantly, with neomycin only. Water intake decreased with the different antibiotics.

1. The effects of intravenous infusions of emulsified cod-liver oil, Ethive (British Codliver Oils (Hull & Grimsby) Ltd; ethyl ester fraction of cod-liver oil rich in polyunsaturated acids) and soya-bean oil on the secretion of milk fat and the composition of blood lipids in the dairy cow were investigated.

2. Soya-bean oil increased the yield of total fat, by increasing the secretion of unsaturated C18 acids in milk and also increased the proportions of oleic and linoleic acids in the blood plasma triglycerides.

3. Cod-liver oil and Ethive both decreased the yield of total fat and the yields of C14 to C18 acids but had no effect on the yields of C4 to C12 acids in milk. Although the emulsions contained considerable quantities of C20 to C22 acids, which were incorporated into the blood plasma triglycerides, these acids were not secreted in the milk fat.

4. It is concluded that, if the polyunsaturated C20 and C22 acids in cod-liver oil are not hydrogenated in the rumen before their absorption from the digestive tract, they can act directly on the mammary gland, possibly through the inhibition of lipoprotein lipase, to reduce the secretion of long-chain acids in milk. In addition, cod-liver oil may have an indirect effect, through changed volatile fatty acid production in the rumen, on the secretion of short-chain acids in milk.

1. Rates of oxygen consumption and carbon dioxide production were measured in pigs from birth to 3 days of age in an open-circuit system.

2. The mean respiratory quotient (RQ) during the first 6 h following birth was 0.95 in fasted pigs and 0.91 in pigs which were allowed to feed.

3. The RQ fell during the remainder of the first postnatal day to mean values close to 0.85, whether the pigs were allowed to feed from birth or were fasted.

4. From 1 to 3 days of age the RQ had a mean value of 0.79.

5. There was little difference in the RQ of pigs exposed to environmental temperatures of either 32 or 16°.

6. It is concluded that the baby pig is not exclusively dependent on carbohydrate for its energy metabolism.