1. A test was carried out simultaneously in Shinfield, Reading, England, and Columbus, Ohio, USA, using typical British and American rations for growing pigs. The rations were compounded in their country of origin; half of each consignment was used at the home station and the other half shipped to the overseas station. 2. Both restricted feeding and ad lib. feeding methods were used at each station. 3. A similar pattern of results was obtained at Shinfield and Columbus. Pigs receiving the American ration, which was higher in energy content, grew faster and required less feed per kg live-weight gain than pigs receiving the British ration. The higher energy content of the ration was probably responsible also for the poorer carcass quality of the pigs receiving the American ration, particularly the high fat content. The comparison between restricted feeding and ad lib. feeding was not affected by the type of ration. Restricted feeding resulted in slower growth rate, slightly better efficiency of feed conversion and considerably better carcass quality.

1. Nine experiments, each with one of six sheep with cannulated rumens given a constant diet of dried grass, were made in which oleic, linoleic or linolenic acid was infused into the rumen and energy and lipid metabolism were measured. One experiment was made in which palmitic acid was given. 2. Judged by changes in the composition of isolated fatty acids, the unsaturated fatty acids were hydrogenated in the rumen. An increase in the excretion of lipid in the faeces occurred when the unsaturated acids were given. The heat of combustion of the faeces increased by 12.6±3.0 kcal/100 kcal fatty acid, of which 94% was accounted for by the additional lipid. 3. Methane production fell when the unsaturated fatty acids were infused, the decreases being 13.8±1.6 kcal CH4;/I00 kcal oleic acid, 14.2±1.5 kcal CH4/100 kcal linoIeic acid and 16.4±1.3 kcal CH4/100 kcal Iinolenic acid. The introduction of a double bond into an n-alkyl acid was calculated to reduce methane production by 0.24±0.09 moles/mole double bond. 4. Because the depression of methane production on infusing the fatty acids exceeded the increase in the heat of combustion of the faeces, the metabolizable energy of the fatty acids was 104.1±5.3% of their heat of combustion. 5. The efficiencies with which the fatty acids were used to promote energy retention were 74.6±5.7% for oleic acid, 79.2±2.0 % for linoleic acid and 82.5±3.0% for linolenic acid. These efficiencies agreed with those noted in experiments by others with rats, horses and pigs given glycerides, but were higher than those noted by others when glycerides were added to the diets of ruminants.

1. Six groups of three (Expt 1) or four (Expt 2) female litter-mate Large White pigs were allocated after weaning to three or four treatments in a randomized block design. 2. In Expt 1, 600ppm copper were added to diets based on maize meal and containing either soya-bean meal, dried skim milk or white-fish meal to provide 16% total crude protein. Severity of Cu toxicosis was assessed by estimating aspartate transaminase (AST) activity in serum, Cu levels in serum and liver, haemoglobin concentration and the incidence of jaundice. 3. Toxicosis was severe only in pigs receiving white-fish meal, but liver Cu and haemoglobin levels were similar in all groups. 4. In Expt 2, 0, 250 or 425 ppm Cu or 425 ppm Cu+150 ppm zinc+150 ppm iron were added to the maize-white-fish meal diet from which the normal Zn and Fe supplements were omitted, creating optimal conditions for development of Cu toxicosis. 5. In the absence of Zn and Fe supplements, 425 ppm Cu caused the development of a severe toxicosis. Simultaneous addition of Zn and Fe supplements eliminated all signs of toxicosis. 6. Under the same conditions 250 ppm Cu caused a mild toxicosis and also exaggerated the slight signs of parakeratosis or Zn deficiency noted in control animals. 7. High calcium levels of 1.7% in a basal diet containing 30 ppm Zn probably induced a marginal Zn deficiency which favoured the development of Cu toxicosis. Differences in calcium level were probably responsible for the apparent effects of the different protein supplements in Expt 1. 8. Occasional occurrences of toxicity in pigs given 250 ppm Cu as a growth stimulant may be partly due to the use of diets low in Zn and Fe and high in calcium. Correcting these factors would extend the safety of Cu supplementation of the commercial diets.

1. In a study of the microbial population in the rumen contents of sheep fed on a semipurified or a roughage-concentrate diet, the total counts and morphological groups of bacteria and protozoa, the counts of proteolytic, amylolytic and cellulolytic bacteria and the rates of breakdown of cellulose and starch in vitro were determined. Three sheep received each diet. 2. Protozoa disappeared completely from the rumen of sheep fed on the semi-purified diet. High counts of Entodinia persisted in the rumen of two sheep on the roughage-concentrate diet; a third animal was maintained defaunated on this diet. 3. The mean total counts of bacteria per g of rumen contents were 5 x 1010 and 2.5 x 1010 respectively in sheep fed on the semi-purified and roughage-concentrate diets and 11.4 x 1010 in the defaunated sheep. 4. The proportions of the morphological groups of bacteria and the counts of amylolytic bacteria were similar with both diets; the mean counts of proteolytic and cellulolytic bacteria were twice as high in the sheep on the semi-purified diet. The counts of all three functional groups of bacteria were considerably higher in the single defaunated sheep. 5. The mean rates of cellulose breakdown were 16.6 and 9.5 g/l. rumen fluid per 24 h for the sheep fed on the semi-purified and roughage-concentrate diets respectively. The corresponding rates of starch fermentation were 28 and 42.4 g/l. rumen fluid per 24 h. 6. It is concluded that the bacterial population in the rumen of sheep fed on the semi-purified and the roughage-concentrate diets differed quantitatively rather than qualitatively. It is also concluded that the absence of protozoa, rather than a direct nutritive effect of the semi-purified diet, was responsible for the increased bacterial population in the rumen of the sheep fed on the semi-purified diet. The much higher bacterial counts in the rumen of the defaunated sheep support this view.

1. Thirty wether sheep comprising five of each of the following breeds, Scottish Blackface, Welsh Mountain, Cheviot, Suffolk Down, Kent and Hampshire Down, were subjected to a standard series of experiments in which energy metabolism was measured during fasting and at the maintenance level of nutrition, and in which maximal voluntary intake of food was measured and the metabolic responses to the stress of wind (10 miles/h) and rain (1 cm/h) were determined. 2. The weight of an individual sheep at the maintenance level of feeding was 8.4% greater and when given feed ad lib. 22% greater than its weight when fasted. These increases largely reflected changes in the weight of gut contents. 3. When fasting metabolism was expressed per kg weight raised to the power 0.73, the small Welsh Mountain sheep had the lowest metabolism of 54.1 kcal/kg W0.73 and the Cheviot sheep the highest of 64.4 kcal/kg W0.73. Overall breed differences were statistically significant (0.05 > P > 0.01). Evidence collected in the experiments, however, suggests that fasting metabolism was more closely related to body-weight raised to the power 0.85. When this basis for breed comparison was used, differences in fasting metabolism between breed groups disappeared. 4. No differences between breed groups in the proportion of the energy they ingested which was lost in faeces, in urine or as methane, were found when they were given food at a maintenance level. The Welsh Mountain sheep, however, had the smallest heat production at the maintenance level when expressed as kcal/kg W0.73. 5. No differences between breed groups in the apparent digestibility of the energy of feed given ad lib. were found. The voluntary intake increased with weight of sheep. When the amount of feed energy consumed and the energy apparently digested were related to the determined maintenance requirement for apparently digested energy of each sheep, no differences between breed groups were found. The efficiency of feed utilization by these breed groups of sheep when given feed ad lib. was the same. 6. It was found that the Hampshire sheep were the most resistant to the effect of wind on their heat production, and the Welsh Mountain sheep the least. The Scottish Blackface was most resistant to the effect of rain on heat production. 7. It is concluded that metabolic differences between different breeds of sheep differing widely in size are quite small, but that breeds differ markedly in their resistance to environmental stresses caused by wind and rain, and that these largely reflect the characteristic fleece types of the breeds concerned.

1. Twenty-four Ayrshire bull calves were reared on either high-concentrate or high-roughage diets to study the effect of diet on the subsequent ability of the calf to digest either concentrates or hay when given alone. The rearing diets were known to produce different types of rumen development. 2. Although there were significant differences between the apparent digestibility coefficients of the high-concentrate and high-roughage rearing diets and between concentrates and hay when given alone, the subsequent ability of the calf to digest either concentrates or hay was unaffected by the type of diet given during the rearing period to 13 weeks of age. 3. The amount of nitrogen retained was significantly greater in calves reared on the high-concentrate diet than in those given the high-roughage diet, but similar amounts of N were retained/100 g gain in body-weight in both groups. After the change in diet, the amount of N retained was significantly greater in calves given concentrates after a rearing diet high in concentrates than in those given concentrates after a rearing diet high in roughage, although in both groups 32% of the N intake was retained. Four of the six calves given hay after a rearing diet high in concentrates were in negative N balance, but only one calf lost weight. Only 19% of the N intake was retained in calves given hay after being reared on a high-roughage diet. 4. The concentration of total volatile fatty acids (VFA) in the rumen contents rose to reach peak levels at about 3 h after food was offered; the concentration then declined. VFA concentrations tended to be higher in calves given the rearing diet high in concentrates than in those given the one high in roughage, and differences reached significance when the diet was changed to one of all concentrates or all hay, with no obvious carry-over effect of the rearing diet. The proportion of propionic, butyric and higher acids tended to be greater in calves given high levels of concentrates than in those given high levels of hay and also tended to rise, irrespective of diet, as the concentration of total VFA rose. 5. A change of diet at 14 weeks from one high in concentrates to one consisting entirely of hay resulted in a significant decline in the viable counts of streptococci, lactobacilli and coliform organisms in the rumen liquor at 16 weeks. The numbers of bacteria were unaffected by the other dietary changes. 6. The concentration of total VFA in plasma of peripheral blood tended to be higher in calves given the high-roughage or all-hay diets. A fall in the concentration of plasma VFA occurred when calves were changed from a high-roughage diet to an all-concentrate diet and a rise in concentration was observed when an all-hay diet replaced one containing a high proportion of concentrates. 7. During the initial rearing period the mean blood plasma glucose concentration was 92.8 mg/100 ml in calves given the high-concentrate diet, a value significantly higher than the mean value of 64.5 mg/100 ml found in calves given the high-roughage diet. The concentra- tion of plasma glucose rose to 89.8 mg/100 ml in calves changed from the high-roughage diet to concentrates and declined to 81.7 mg/100 ml in calves that were given hay in place of the high-concentrate diet. 8. The weight of contents of the reticulo-nunen and omasum and the volume displacement of these organs were significantly greater in calves given hay as the sole diet during the last 3 weeks of life than in those given concentrates during this period. The weight of tissue forming the reticulo-rumen was significantly greater in calves given the all- concentrate diet during the last 3 weeks of life than in those given only hay during this period. It was apparent that the rumen papillas developed rapidly in those calves given concentrates as the sole diet for a period of 3 weeks after a rearing diet high in roughage, whereas there was a marked retrogression of papillas when concentrates were withdrawn from the diet. 9. It is concluded that the ruminant calf adapts readily to marked dietary changes, with the result that differences in the size and structure of the ruminant stomach, which have been shown to occur when different types of diet are given, have no permanent effect on the ability of the calf to digest diets of concentrates or hay.

1. Six groups of four litter-mate female Large White pigs of about 17 kg live weight were allocated according to a 2×2 factorial design in each of two experiments in which rations containing 0 or 750 ppm copper were offered with either 0 and 500 ppm zinc, or 0 and 750 ppm iron. 2. Severity of toxicosis was assessed by determining aspartate transaminase activity in serum, observing the incidence of jaundice and determining the hemoglobin concentration in whole blood and Cu concentration in serum and liver. 3. Addition of 750 ppm Cu to the diet caused toxicity in nine out of twelve animals; it was most severe after about 4 weeks when two-to five-fold increases in serum Cu and aspartate transaminase levels were found and seven pigs were jaundiced. Serum Cu and aspartate transaminase concentrations and degrees of jaundice were apparently interrelated and returned to normal levels after 6 weeks, suggesting adaptation to the high Cu intake. Growth depression and a microcytic hypochromic anaemia persisted. 4. Addition of 500 ppm Zn or 750 ppm Fe in the presence of 750 ppm Cu eliminated jaundice and produced serum Cu and aspartate transaminase concentrations similar to control values after 4 weeks. Only supplementary Fe afforded protection against anaemia. 5. Variability in the response of the pig to Cu supplements could be partly due to variations in the intake of Fe and Zn. The addition of Fe and Zn supplements to pig diets supplemented with Cu would probably reduce the small risk of causing Cu poisoning.

1. A preliminary study was made of chewing duringeating with a total of sixcows with rumen fistulas, given diets of hay or herbage. A sieving technique was used to determine the size of particles of food swallowed at intervals throughout the eating period. The number of jaw movements, number and weight of the swallowed food boluses and the time spent eating were measured with each diet.

2. The mean particle size of hay contained in a bolus collected at the cardia varied between individual cows from 1602 μm to 1244 μm. Boluses swallowed in the first few minutes of eating contained particles of a larger average size than those at any other time during the meal. Also, the rate of swallowing boluses of food was much faster at the beginning of a meal and the weight of boluses smaller than at any other time. The frequency of jaw movements did not vary appreciably during a meal.

3. Increasing the amount of hay given to the cows by 50 % or giving a different hay did not cause any significarlt alteration in the average size of particles of swallowed hay, and changes in the rate of swallowing boluses, or in, the rate of jaw movements and the size of boluses were not very marked.

4. With a diet of herbage, boluses were swallowed rapidly and the average particle size of swallowed food was larger than that of hay. Also, there were slightly more jaw movements per min and larger boluses than with hay.

5. The observations made in the study are discussed in relation to possible factors that determine the particle size of swallowed food.

1. A comparison of the distribution of radioactivity in rat tissue lipids after oral administra- tion of [5-Me-14C]-α-tocopherol showed that spleen and adrenal lipids have a relatively high uptake of radioactivity. 2. Absorbed α-tocopherol and its metabolites appeared not to re-enter the lumen of the gut in significant amount through the bile or by the secretion from the stomach mucosal cells within the 24 h experimental period. 3. After ingestion of [5-Me-14C]-α-tocopherol by rats, analyses of their liver and spleen lipids showed that most of the radioactivity in the lipids was due to the presence of unchanged α-tocopherol. Radioactive tocopherolquinone was found in both spleen and liver lipids; in the liver lipids there was some evidence that a second oxidation product of α-tocopherol, compound O, had been formed.

1. Prolonged intermittent exposure to reduced environmental temperature (+2°) produced in rats given a nutritionally well-balanced diet a decrease in the concentration of esterified fatty acids in the blood serum, liver and epididymal fat tissue. In the last there was a significant increase in the unesterified: esterified fatty acid ratio. The hepatic synthesis of fatty acids from [1–14C]acetate remained unchanged. A decrease in the concentration of cholesterol was found in the blood serum, liver and lungs of animals exposed to cold.

2. When a high-fat, high-cholesterol diet was given, exposure to cold increased the mobilization of lipids; this was indicated by the elevation of the unesterified fatty acid levels in the blood serum and in the epididymal fat tissue. In rats given the high-fat diet the lipotropic action of cold on the liver was confirmed. This action was characterized by a decrease of esterified fatty acid levels and by an increase of glycogen concentration in the liver. This effect is probably due to a lowering of hepatic lipogenesis and to increased oxidation of fatty acids in the liver tissue. In rats given the high-fat dict, cold exposure produced an increased cholesterol accumulation in the tissues and more pronounced morphological changes in the myocardium.

1. Monozygotic twin cattle were used in a preliminary study of the effect of pregnancy and of lactation on the voluntary intake of food and water, and on eating and ruminating behaviour. Also, results are reported of an experiment with five pairs of monozygotic twin heifers to examine the variation within pairs of twins in voluntary intake of food and water and eating and ruminating behaviour.

2. Voluntary food and water intakes were measured during the last few weeks of pregnancy and during early lactation. Within each twin pair one twin was pregnant or lactating and the other non-lactating and not pregnant, and the food and water intakes of a pair of twins were measured simultaneously.

3. On average the variation in voluntary intake of hay within pairs of non-pregnant, monozygotic twin heifers was 0.2 kg or 3 % of the mean daily hay intake.

4. The effect of pregnancy was observed in six pairs of twins and in five of the pairs the pregnant animal ate iess hay than its non-pregnant twinmate; in four of these five pairs the effect was small (13 % ). Changes in eating and ruminating behaviour associated with pregnancy were small; the pregnant animals ate concentrates and hay more slowly and ruminated longer than the non-pregnant animals.

5. Lactation was associated with a mean increase of 29 % in hay intake in eight out of the nine pairs studied. In four pairs of twins given a diet of concentrates alone the lactating animal ate on average 8 % more than the non-lactating animal. The lactating cows tended to eat concentrates and hay more quickly than the non-lactating cows; because of differences in the ratio of hay to concentrates it was not possible to interpret the changes in rumination that occurred with lactation.

1. The diets of sledge dogs at a British Antarctic sledging base were studied both at base and during sledge journeys, and samples of the diets and the relevant faeces were analysed. Changes in weight were related to calorie intakes.

2. The calorific requirements of sledge dogs were found to vary considerably from dog to dog and depended on the activity in which the dogs were involved. Whereas 2500 kcal/dog daily were just sufficient to maintain the body-weight of a completely idle dog, 5000 kcal/dog were insufficient to maintain the body-weight of a dog pulling a heavy sledge over long distances.

3. Seal meat was found to be the most beneficial and most satisfactorily absorbed diet. The artificial diets, pemmican and Nutrican, were adequate to maintain body-weight if sufficient supplies were available to give dogs as much as twice the routine ration, but were uneconomical in that large quantities of nutrients were passed in the faeces.

1. Beef fat oxidized to a peroxide value of 109 μmoles/g (218 m-equiv./kg), with a reduction in iodine value of 3.4 units, was incorporated at a 5% level in the diet of day-old chicks (diet 2) and stored for 8 weeks at room temperature during feeding. Similar diets containing fresh fat (diet 1, peroxide value zero) or oxidized fat in which the peroxide had been largely destroyed by heating (diet 3, peroxide value 2 μmoles/g) were also used. The diets contained adequate but not excessive levels of all vitamins, including stabilized vitamin A, except that for half of the chicks the supplement of stabilized vitamin E was omitted. 2. No further oxidation of the dietary lipid occurred during storage, and the initially high peroxide value in diet 2 decreased rapidly. The natural vitamin E decreased by more than 50% in diet 2, but remained unaffected in diets 1 and 3. 3. The chicks grew normally, with no difference in weight gain or feed conversion between the groups, the only differences attributable to the diets being marginally lower vitamin A levels accumulated in the livers of the birds on diet 2 and ajustdetectablyhigher liver weight in the birds on diet 3. 4. One of the twelve chicks receiving oxidized fat (diet 2) without synthetic vitamin E developed encephalomalacia. There was no other suggestion of performance being inferior as a consequence of the absence of the vitamin E supplement. 5. No difference could be detected in the flavour of the chickens, either freshly roasted or reheated.

1. A comparative study has been made of five methods of saponifying normal and vitamin E-deficient rat liver and subsequently measuring ubiquinone and α-tocopherol. 2. Losses of ubiquinone and α-tocopherol occur under certain conditions, and three of the methods were judged to be unsatisfactory. Recoveries of α-tocopherol are nearly quantitative under the conditions of ToŠić & Moore (1945), but methods that use large reaction times or weaker alkali destroy tocopherol, and over 50 % loss can be encountered. Ubiquinone does not seem as sensitive to the time of reaction, but is sensitive to the concentration of alkali and amount of water present during saponification.

1. The effect of dietary protein level and supplementation with thyroxine and thiouracil on depletion of liver stores of vitamin A, on the percentage of liver vitamin A in the alcohol form and on the plasma level of vitamin A and protein has been studied in chicks. In an experiment with cockerels the relation was investigated between the vitamin A level of plasma and the electrophoretic pattern of its proteins.

2. Liver vitamin A depletion was considerably reduced by lowering the dietary protein level.

3. Protein malnutrition lowered the percentage of vitamin A found in the liver in the alcohol form.

4. Depletion of vitamin A from the liver was related to the percentage of vitamin A in the alcohol form.

5. Thyroxine increased both vitamin A depletion from the liver and the percentage of vitamin A in the alcohol form, whereas thiouracil had the opposite effect.

6. Plasma vitamin A, and plasma protein contents were significantly lowered in cockerels receiving a 5% protein diet. The drop in plasma protein level was essentially caused by a reduction of the albumin fraction. No significant change in the levels of globulins was observed even after a 4-week period of protein malnutrition.

7. When the dietary protein level was restored to normal both the albumin and vitamin A levels in plasma increased.

1. The metabolism of seventeen steers was determined on forty-nine occasions during fasts of either 112 or 136 h duration.

2. Faeces continued to be produced during fasts of up to 136 h duration at rates which were 15–20% of those noted before the fasts began.

3. Carbon dioxide production and oxygen consumption fell continuously throughout with animals weighing less than 200 kg but changed little after 88 h in animals weighing more than 200 kg. Methane production was considerably reduced during fasting but did not disappear. Urinary nitrogen excretion changed very little. Of the total loss of energy from the body, the loss of protein accounted for 25%. This was unaffected by age or size of animal.

4. With individual Ayrshire steers, metabolism increased during growth with body-weight raised to the power 0.68±0.05. No greater precision of estimate was obtained from logarithmic regressions of metabolism on body-weight than from linear ones.

5. Seven Ayrshire steers had a mean fasting metabolism of 100±1.6 kcal/kg W0.73 24 h, eight Black cattle of the Aberdeen Angus type a fasting metabolism of 81±1.5 kcal/kg W0.73 24 h and two Ayrshire x Beef Shorthorn steers a fasting metabolism of 96±2.9 kcal/kg W0.73 24 h. Variation in the fasting metabolism of an individual steer from time to time, expressed as a coefficient of variation, was ±7.4%.

6. The results are discussed in relation to interspecies generalizations about the relation between fasting metabolism and body-weight.

1. Turkey poults were fed from day-old to 6 weeks on a practical-type diet containing 10 % white fish meal (supplying 0.7 % lipid) and other constituents, mainly cereals (supplying 3.3 % lipid), together with either 1.5 % of anchovy oil that had been allowed to autoxidize under various conditions or 1.5 % of fresh beef fat.

2. For group I the whole diet with anchovy oil was stored in air at 15° for 3 months before feeding. Its lipid oxidized only slowly, with no appreciable rise in peroxide value and little destruction of its polyunsaturated fatty acids. For groups 2 and 3 the anchovy oil was mixed with the white fish meal, and the mixture was stored for 3 months, by which time most of its polyunsaturated fatty acids had been destroyed by autoxidation and the pv of the extractable lipid, after reaching a peak of 260 μmoles/g, had fallen again to 110. At this point the anchovy oil-fish meal premixture was further mixed with the basal diet and used, either immediately (group 2) or after 3 months' further storage (group 3). 3. The turkeys in all three groups receiving ‘fish oil’ remained healthy and grew well, with only slightly apparent (and not significantly) lower weight gains than those on the control diet. There was no significant treatment effect on liver weight, serum aspartate amino-transferase or serum alanine aminotransferase activity. All the birds stored vitamin A in their livers, though the diets had provided not more than adequate supplies of this vitamin, but the reserves accumulated were significantly lower when the diets contained oxidized fat. On roasting, the turkeys of group 1 had a definite and objectionable fishy flavour, whereas those of groups 2 and 3 were as palatable as the controls on the beef fat diet.

1. Groups of male rabbits (ten to thirteen per group survived) were given ad lib. a diet consisting of 80 parts of a low-fat basal diet to which were added: for group I, 20 parts maize oil; for group 2, 20 parts butterfat; for group 3, 10parts maize oil and and 10parts butter- fat; for group 4, 0.47 parts maize oil and 43.1 parts wheat starch; and for group 5, 10.2parts maize oil and 21.6 parts wheat starch. The animals in group 6 were givenan ordinary com- mercial rabbit diet. 2. The rabbits were given the various diets for 38 weeks, after which a sample of blood was taken. The rabbits were then killed and the liver and a sample of perine- phric adipose tissue were removed from each animal. The plasma, liver and adipose tissue lipids werefractionated on columns of Florisil and the fatty acid compositions of the tri- glyceride and unesterified fatty acid fractions were determined by gas-liquid chromatography.

3. The effects of the different diets on the composition of the unesterifiedfatty acids in the plasma were very similar to the effects of the diets on the fatty acid composition of the plasma triglycerides, but in the plasma unesterified fatty acids the concentration of stearic acid was consistently higher and the concentration of linoleic acid was consistently lower than in the plasma triglycerides. 4. There appeared to be a positive rectilinear relationship between the concentration of stearic acid in the plasma triglycerides and the concentration of triglycerides in the plasma. 5. In the triglycerides of the plasma, the concentrations of palmitic and stearic acids were consistently greater and the concentration of linoleic acid was consistently less than the corresponding concentrations of these fatty acids in the triglycerides of the adipose tissues. In the two groups of rabbits given low-fat diets the fatty acid composition of the liver trigly- cerides was almost identical with that of the plasma triglycerides. 6. In each of the six groups of rabbits the composition of the unesterified fatty acids in the plasma was identical with that of the unesterified fatty acids in the adipose tissues. Inthe unesterified fatty acids of the liver the concentrations of linoleic andarachidonic acids were consistently greater and the concentrations of myristic, palmitic and palmitoleic acids were consistently less than the corresponding concentrations of these acids in the unesterified fatty acids of the plasma and adipose tissues. 7. The results of this investigation are discussedin the light of recent con-cepts on the metabolic relationships between the unesterified fatty acids and triglycerides of the liver, plasma and adipose tissues.