1. When rumen fluid together with small quantities of (15NH4)2S04 [1-14C]sodium acetate and polyethylene glycol (PEG) was introduced into the emptied rumen of a sheep, no significan change occurred in the ratio 15N:14C during a period of 30–60 min. The ratio 15N:PEG, however, declined by 22–53%. when(15NH4)2SO4, [1-14C]sodium acetate and PEG were introduced into the normal rumen of a sheep fed on lucerne hay the ratio 15N:14C in the whole rumen contents showed no appreciable change in a period of 1 h, but the ratio 15N:PEG declined by 25–41%. It was therefore concluded that the rate constants for removal of ammonia nitrogen (NH2-N) and volatile fatty acid (VFA) from the rumen were very nearly equal.

2. In sheep fed at 1 h intervals on lucerne hay chaff or lucerne hay pellets VFA production, VFA and NH3-N concentration in the rumen fluid and the volume of fluid passed from the rumen to the omasum were determined. From these results and the information previously gained on the relative rates of removal of NH2-N and VFA from the rumen, the amounts of NH3-N produced in the rumen and absorbed there or at lower levels of the digestive tract were calculated to be equivalent to 23–27% of the dietary N in lucerne hay chaff and 17% of that in lucerne hay pellets; 59–66% of the NH3-N was absorbed from the rumen and the remainder passed to the omasum.

1. The respiration rate of ova during their early cleavage stage from two groups of rats reared on diets of NDpCal% 10 or NDpCal% 5 has been measured, using a Cartesian diver.

2. Measurements from twenty-six experiments show that the average oxygen uptake of ova from the rats reared on the diet of high protein value was 0.563±0.175 mμl O2/ovum per h and the value for rats reared on the diet of low protein value was 0.440±0.076 mμl O2/ovum per h when measurements were made in a medium containing 0.9% NaCl and rat serum or plasma (2:1). The difference between these results was significant at 0.05 > P > 0.02.

3. It is suggested that the lower respiration rate of ova from rats maintained on the diet of low protein value may be due partly to the effect of dietary protein deficiency on conditions within the Fallopian tube and partly to the eRect on the maturation of the ovum itself.

1. Fluids were given by mouth in various ways to young sheep. The extent to which closure of the oesophageal groove operated to direct the fluid to the abomasum was assessed by radiography.

2. Salt solutions and milk given as a drench did not produce complete closure of the groove. However, when the animals were accustomed to sucking from a teat before weaning, any liquid suspension and also water, sucked from a bottle, passed entirely to the abomasum even in 12-month-old sheep.

3. This technique may be useful when it is desirable to cause protein or other nutrients to by-pass fermentation in the rumen.

1. A femur was analysed from each of the following malnourished children: five Turkish (4–7.5 months; marasmic), eight Jamaican (9–13 months; two marasmic, one marasmic with kwashiorkor, three with kwashiorkor, two ‘malnourished’) and two Ugandan (11 and 12 months; marasmic and with kwashiorkor respectively). These were matched with appropriate controls. Dry weight, fat, total nitrogen, collagen N, calcium and phosphorus were determined, and values are presented for them in the bone, with and without epiphyses, and in the epiphyses and cortex.

2. The femurs of the Turkish children (4–7.5 months) showed greater deficits in length, Ca and P than did those of the Jamaican and Ugandan children (9–13 months). In both age-groups, regardless of the clinical condition, there was significantly less dry fat-free bone tissue than in control bones of similar ages. The concentration of fat in the bones was variable, but in the Turkish bones it was higher than in the controls.

3. When the epiphyses were excluded, the femurs of the Jamaican and Ugandan children with kwashiorkor contained a lower concentration of total N per 100 g fat-free solids than did those of children with marasmus.

4. The epiphyses of the malnourished children aged 4–7.5 months contained lower concentrations of total N, collagen N, Ca and P than those of controls. In the older age-group the only significant difference was a lower level of Ca.

5. The cortex of all the malnourished children had a similar composition to that of the controls.

1. The fermentation of twenty-six different carbohydrates was studied in an artificial rumen.

2. The rates of fermentation varied widely, but except in the case of rhamnose the amount of methane produced was usually related to the amount of carbohydrate fermented (6.0 Cal/ 100 cal of substrate). There was also a correlation between the amount of carbohydrate fermented and the amounts of steam-volatile acids formed.

3. Glucose, fructose and sucrose were fermented rapidly but mannitol, sorbitol, glucuronic and galacturonic acids, glucosamine, D(–)-arabinose, ribose, sorbose, trehalose and starch were fermented very slowly or not at all. L(+)-Arabinose, xylose, galactose, mannose, cellobiose, maltose, lactose, raffinose, inulin, xylan and pectin were fermented at appreciable rates.

4. The methyl-pentose, rhamnose, was fermented but no methane was produced. Fucose was fermented very slowly.

5. The fermentation of sucrose and its constituent hexoses was characterized by a transient accumulation of lactate. The fermentation of rhamnose and of glucosamine was accompanied by permanent accumulation of lactate. No measurable amounts of lactate were produced when any of the other sugars were fermented.

1. Samples of subcutaneous (inguinal) and perinephric adipose tissue were obtained, at slaughter, from each of twenty male calves. Three were neonatal animals, three were 3 days old and two were fed on reconstituted milk to appetite until they weighed 100 kg. The other twelve calves were given milk until they reached 50 kg live weight; concentrates were then included in the diet until, at 60 kg live weight, six calves were slaughtered. The remaining six calves were raised to 100 kg on concentrates alone. The weight of the empty reticulo-rumen of each slaughtered calf was recorded.

2. The component fatty acids of the adipose tissue triglycerides of the neonatal and 3-day-old calves were very similar; about 80% consisted of oleic acid (18:1) and palmitic acid (16:0) and the remainder comprised stearic acid (18:0), palmitoleic acid (16:1) and myristic acid (14:0), together with very small amounts of other acids which, in the glycerides of the 3-day-old calves, included some evidently of colostral origin. The perinephric glycerides of both these groups of calves were somewhat more unsaturated than were those of subcutaneous adipose tissue.

3. The continued consumption of milk by the calves slaughtered at 60 kg live weight was reflected in the presence of enhanced proportions of 14:0, 18:2, 17:0 and 17:1 in the depot triglycerides and, in addition, very small amounts of branched-chain acids and trans 18:1 were detected. A similar fatty acid pattern was observed in the triglycerides of the calves which were given milk only until they were 100 kg live weight. In all these calves only limited growth of the rumen took place.

4. By contrast, the calves which were raised on solid feed from 60 kg to 100 kg and in which rumen development had taken place had depot triglycerides whose fatty acid composition resembled that found in adult animals. Increased proportions of stearic acid accompanied by relatively large amounts of trans 18:1 were present, evidently as a result of the assimilation of the products of bacterial modification of dietary fatty acids in the rumen.

5. Regardless of the age of the calves and the over-all fatty acid composition of their tissue triglycerides, the intramolecular disposition of the fatty acids was similar in that saturated components were present esterified mainly in positions 1 and 3, and unsaturated acids for the most part in position 2; the only major exception to this distribution pattern was in respect of trans 18:1 which, when present, was preferentially esterified to the primary alcoholic groups of the glycerol moiety as if it were a saturated acid.

1. Experiments on three pairs of male identical twin calves have shown that underfeeding at 2.5–6 months of age, i.e. during the critical stage of sexual maturation, considerably delayed the process of puberty, as regards testicular androgen production as well as secretion of fructose and citric acid by the seminal vesicles.

2. There was no marked difference in the blood-plasma content of non-protein nitrogen, vitamin A and carotene at 6 months, as between twins on a normal (N) and low (L) plane of nutrition, although the L-twins were growing and maturing more slowly. However, the blood-plasma content of glucose and of most of the free amino acids, was slightly reduced as a result of underfeeding.

3. When at the age of 6 months two twin-pairs were castrated and injected with either testosterone or androstenedione (50 mg every 3rd day, for 2 months), the L-twins of both pairs and the N-twin of one pair grew at a faster rate. Moreover, the concentration of nitrogen in blood plasma increased, the rise being particularly evident in the content of indispensable amino acids. This effect, however, was more pronounced in the N- than in the L-twins.

4. Testosterone treatment enhanced libido in the N-twin but not in the corresponding L-twin. Androstenedione had no effect on libido in either the N-twin or the L-twin. Thus, although testosterone and androstenedione both effectively promoted growth and nitrogen metabolism, androstenedione, unlike testosterone, was devoid of androgenic activity.

1. The effect of riboflavine deficiency on liver ribonuclease activity, RNA and DNA content, and 32P incorporation into RNA and DNA has been studied in rats maintained on a 16% protein diet, a protein-free diet and on a protein-free diet subsequently replaced with a 40% protein diet.

2. Rats maintained on a riboflavine-deficient diet for 45 days showed decreased incorporation of 32P into liver RNA but no effect on the RNA content of liver. The concentration of DNA in liver and 33P incorporation into it remained unaffected. After a deficiency period of 70 days, both the RNA and DNA contents of liver were found to be decreased. When the riboflavine-deficient or control rats were given the protein diet for 30 days and then a proteinfree diet for 15 days, the RNA content of their livers decreased, while the liver DNA content was increased. Repletion with a 40% protein diet restored the RNA and DNA content in both control and riboflavine-deficient rats.

3. Liver ribonuclease activity was decreased after a deficiency period of 45 days, whereas it was increased after a deficiency period of 70 days.

4. A correlation between liver RNA level and liver ribonuclease activity in riboflavine deficiency is suggested.

1. Weanling rats were fed on an iron-deficient diet without added folic acid and litter-mate controls received the same diet supplemented with Fe. Groups of deficient and control animals were killed at intervals of up to 88 days and glutamate formiminotransferase activity in liver and folic acid activity in liver and serum were measured.

2. No differences were found between the results from the deficient and control animals, although the deficient diet produced marked falls in haemoglobin, packed cell volume and serum iron.

3. In a second experiment folic acid was added to the diets and twelve rats received the Fe-deficient diet and their litter-mates were fed on the Fe-supplemented diet for 91 days. No differences were found in the activity of glutamate formiminotransferase purified from the combined livers of the two groups.

1. Procedures, based on those of Schmidt & Thannhauser (1945) and Schneider (1945), for the extraction and estimation of nucleic acids in bovine digesta were examined in detail.

2. Final methods which were suitable for routine determination of RNA and DNA were essentially as follows. Digesta samples were extracted in the cold, first with a solution of trichloroacetic acid in ethanol, then with aqueous trichloroacetic acid solution and finally with lipid solvents. The dried residue was hydrolysed with alkali, purified by passage through a Dowex resin, and the RNA, in the form of mononucleotides, determined by U.V. absorption. DNA was determined separately in hot perchloric acid extracts of the original dried residue by colorimetric estimation of the deoxyribose content.

1. A study was made of the partition of the major constituents of rat's milk during the formation of the clot in the infant rat's stomach.

2. Milk was obtained from the dams by manual expression after separation from their litters for periods ranging from 12 to 23 h.

3. The ratio of fat to protein in the clots removed from the stomachs of the 11-day-old pups was more than double that found in the milk. The difference was due to the high fat content of the clot.

4. The stomach contents of DUDS which were allowed to suckle for I h following a 12 h separation from their dams had fat to protein ratio similar to that of the expressed milk, When suckling was prolonged, the ratio reverted to that of the established clot.

5. Milk secreted under conditions of uninterrupted lactation and promptly recovered from the stomachs of pups previously fasted had a value for fat to protein comparable to that for the clot from a normally fed pup. An interruption in suckling therefore reduced the fat content of the milk.

6. Part of the carbohydrate in rat's milk is secreted in a bound form. Lactose accounts for approximately one half of the total carbohydrate. Evidence is presented which suggests that the remainder may be an isomer of lactose.

7. Fat and lactose undergo hydrolysis to a small extent only in the pup's stomach. The breakdown of protein is insignificant. Rat's milk contains no proteolytic enzymes.

8. No significant differences in composition were found in the outer shell, the core and pyloric regions of the clot. Thus fat and casein leave the stomach in constant proportion.

1. Six adult, non-pregnant, non-lactating, Friesian cows were used when fat and when thin to measure differences in the voluntary intakes of straw, hay and hay plus concentrates caused by the fatness of the animals. Measurements of digestibility, time of retention of food in the digestive tract, rate of breakdown of cotton threads in the ventral sac of the rumen and amounts of digesta in the reticule-rumen were included.

2. The mean voluntary intakes of straw were similar for fat and thin cows. In absolute terms, thin cows consumed 31 % more hay and 23 yo more hay and concentrates than fat cows; in relation to metabolic body size (W0.75), these differences were 76% and 52% respectively.

3. Small decreases in digestibility of these diets by the thin cows, reflected in slight reductions in the rate of loss of weight of cotton threads placed in the rumen, did not alter the significance of the differences in intake between fat and thin cows.

4. Small changes in time of retention of food in the digestive tract suggested that the capacity of the tract may have been greatest in the thin cows.

5. The presence of a greater amount of digesta in the reticulo-rumen of thin cows than in that of fat cows after eating hay supports the suggestion of a greater gut capacity in these animals. In both fat and thin cows, the capacity of thereticulo-rumen didnot appearto havelimited the intake of the hay and concentrate diet. In both groups the lowest levels of rumen fill were observed after straw was given.

6. The results are discussed in terms of possible mechanisms which may operate to reduce the voluntary intake of medium- and good-quality diets as cows become fatter. When poorquality roughages are given, other factors appear to conceal any differences in intake which may exist between fat and thin cows.