1. Reduced intake of energy or protein per se decreased riboflavin requirement of the chicks under restricted feeding regimens.

2. In severe riboflavin deficiency (2·26 mg/kg diet), efficiency of utilization of both energy and protein was decreased significantly under ad lib. conditions of feeding.

3. Efficiency of utilization of energy (but not protein) was decreased significantly in border-line riboflavin deficiency (3·02 mg/kg diet), when chicks were fed ad lib.

4. Efficiency of protein utilization was decreased significantly in severe riboflavin deficiency when chicks received an energy-restricted diet supplying 80, 70 or 60 yo of the energy intake of the controls.

5. Neither energy nor protein utilization was affected by riboflavin deficiency when both energy and protein were restricted to 70 yo of that consumed by chicks fed ad lib. However, the riboflavin deficiency produced characteristic deficiency symptoms, namely heterophilia, curled-toe paralysis, and reduction in concentration of liver riboflavin.

1. The effect of drying and ensiling ryegrass on the site of digestion of the energy andcarbohydrate fractions was studied in sheep fitted with rumen cannulas and re-entrant can-nulas in the proximal duodenum and terminal ileum.

2. The sheep were given fresh (frozen) grass, dried grass, wilted and unwilted silage pre-pared from herbage harvested from the same sward. The grass diets were offered twice dailyto each animal and paper impregnated with chromium sesquioxide was administered twicedaily into the rumen. Twenty-four hour collections of duodenal and ileal digesta, adjusted togive 100 yo recovery of Cr2O3, were analysed to determine the extent of digestion in the fore-stomachs, the small intestine and the caecum and colon.

3. Total digestibility of the gross energy was similar for the fresh grass, dried grass andwilted silage diets (67·4,68·1 and67·5 %)but higher for the unwilted silage (72·0 %, P < 0·01).There was an increased flow of energy into the small intestine when the sheep were given driedgrass and unwilted silage. The proportion of the apparently digested energy lost within thesmall intestine was greater when the dried grass was given (302 yo) than when the fresh grasswas given (23·6 yo).

4. Drying or ensiling of wilted material affected digestion neither in the entire alimentarytract nor in the different sections of the tract, of some carbohydrate fractions. About 97 yo ofthe digested water-soluble carbohydrate, over 90 yo of the digested cellulose and over 70 yo ofthe digested hemicellulose were digested before reaching the small intestine. The increasedamount of energy entering the duodenum of the sheep given the dried grass was notaccounted for by changes in the fate of these carbohydrate fractions in the digestive tract. Withunwilted silage, digestibilities of the cellulose and hemicellulose fractions were higher, andlower proportions of the digested carbohydrates were lost before the small intestine.

1. The object was toinvestigate the importance of urea a source of ammonia in the large intestine of herbivores. Urea was present in small intestinal contents of slaughtered horses in concentrations similar to those in blood but, in the small intestine of salughtered sheep, the urea was less than in blooc.

2. There was little ammonia in small intestinal contents of slaughtered horses but consider-able ammonia was present in small intestinal contents of slaughtered sheep. The ammonia in small intestinal contents of the slaughtered sheep was probably formed from urea, as ileal con-tents taken from a sheep with an ileal cannula contained considerable urea and little ammonia.

3. The ammonia concentration in caecal contents of sheep was related to the concentration of urea in blood except when ileal contents were prevented from entering the caecum.

4. Ileal digesta of sheep contained more free amino nitrogen than did caecal digesta.

5. Ammonia was absorbed more rapidly than water from the caecum of sheep. The rate of absorption was related to the concentration of ammonia in the caecum.

1. Twenty herbages at different stages of maturity containing from 0·77 to 5·23 g nitrogen/100 g organic matter were harvested, and green herbages were rapidly frozen and stored at - 1·5°. Each herbage was offered at levels approximating to ad lib. to a group of three sheep, individually penned. Intake, digestion and retention of N were studied during a 10 d collec-tion period after a 9 d preliminary period.

2. General regressions relating apparently digested N (NA, g/d), urinary N excretion (UN, g/d) and retention of N (NR, g/d) to N intake (NI, g/d) were established: NA= 0·88NI-3·25 (±1·14; SEb = ±O·013); UN = 2·48+0·35 NI+O·0049 NI2 (±3·09; SEb1, =±0·156; SEb2 = ±0·003); NR = 0·25 NI- 1·92 (±2·40; SEb = ·o·029). These equations accounted for 99% of the variability in N apparently digested, 86% of the variability in urinary N excreted, and 63 % of the variability in N retained.

3. Concentrations of ammonia and trichloroacetic-acid-precipitable N in the reticulo-ruminal digesta and of urea and a-amino-N in plasma were determined immediately before feeding, and at I and 4 h after feeding. Relationships between concentrations of metabolites in the reticulo-ruminal digesta and in plasma, and N intake, N apparently digested, urinary N output and retained N were examined. Estimates of urinary N loss and of retained N based upon metabolite concentrations at individual sampling times were characterized by high residual variabilities. Error terms were in some instances reduced significantly when both thebasal (before feeding) metabolite concentrations and the increments in metabolite concentra-tions after feeding were included in the one equation. The best relationships, based on plasma urea concentrations, accounted for only 74 % of variability in urinary N output.

4. In multiple regressions a significant portion of the variability in urinary N output and in retained N which was not accounted for by N intake could be accounted for by inclusion of metabolite values.

5. The concentration of urea in plasma was the most effective basis for prediction of N utilization. However, no prediction equation accounted for more than 90% of the total variabilityin N output, and no equation accounted for more than 71 % of the total variability in N retention. The feasibility of developing techniques for examination of efficiency of N utilization by a particular class of animal, based upon digesta and plasma metabolite con-centrations is discussed.

1. Eighteen bull calves, comprising twelve Ayrshires, three Friesians and three Jerseys were reared from birth to a slaughter weight equivalent to 22 % of mature cow weight of the breed.

2. All the calves were given a milk substitute diet ad lib. in two feeds daily. Six of the calves received this diet alone and the remaining twelve calves were offered roughage ad lib. from I week of age, either as meadow hay or as barley straw. The calf-house was maintained at a mean temperature of 23' and a mean relative humidity of 62 %.

3. The mean total intake of meadow hay and barley straw over the experimental period of about 12 weeks was 3.0 kg and 0.4 kg respectively. Only three calves were consuming any meadow hay and only two calves any barley straw at 7 weeks of age.

4. The roughage consumed had no effect on the incidence of diarrhoea, on dry-matter intake from milk or on live-weight gain. All the calves offered meadow hay had lung lesions at slaughter. Severity of lung lesions in the Jersey and Friesian calves combined, but not in the Ayrshires, tended to be inversely related to the relative humidity to which they were exposed.

5. Dressed carcass weight and killing out percentage tended to be lower for the calves offered meadow hay. There was a highly significant inverse relationship between total intake of hay and killing out percentage. Perirenal fat depositionin relation to carcass weight was significantly lower and carotenoid content of the fat significantly higher for the calves offered the meadow hay. Skin weight per unit of slaughter weight 0.78 or carcass weight OJ* was significantly greater for the calves given the milk substitute diet only.

6. It is concluded that the calf shows very little desire to eat roughage when given a good- quality milk substitute diet ad lib. and that, even when the amounts of roughage consumed are small, this has a deleterious effect on carcass quality.

1. An attempt was made to measure body volume and body fat in malnourished children using the same closed-circuit apparatus for both determinations. If these measurements were sufficiently accurate, they would enable total body protein to be calculated.

2. A helium dilution technique was used to estimate the volume of the child. Although highly reproducible measurements were obrained for the volume of inanimate objects by this techinque, the results with children were erratic.

3. The fat stores of the child were determind by measuring the amount of cyclopropane (C2H4) which would dissolve in the body. This technique gave acceptable answers with marasmic children who have little subcutaneous fat, but with obese children equilibrium could not be obtained in an acceptably short period of time. It is not practicable to calculate the equilibrium concentration by extrapolation of the uptake curve in obese children.

1. Lambs were removed form their dams at 2 d of age, and at 5 weeks of age eitht of one group were incoulated with a mixed rumen ciliate and seven in a second group were maintained ciliate-free throughout the 61 weeks of the experiment. Performance of the groups was compared when given a 2:1 roughage:concentrate diet as a set ration and with ad lib. roughage.

2. Mixed ciliate populations developed in all faunated lambs and average-sized populations were maintained. Large numbers of flagellate protozoa developed in the ciliate-free animals after flagellates had been introduced into the building with the ciliate-free animals after flagellates had been introduced into the building with the ciliate inoculum.

3. Higher numbers of rumen bacteria were found in the ciliate-free group.

4. Only between the 14th and 21st weeks was there a significant different between groups in weight gain and this was infavour of the faunated group. The only significant different in body measurements was greater girth in the ciliate-free lambs.

5. Only minor differences were found between the groups in calorimetric trials, digestibility and nitrogen balanes. There were no differences between groups in concentration of total protein N and soluble sugar in the rumen. The ammonis concentration was significantly higher in the faunated group.

6. The concentrations of total rumen volatile fatty acids (VFA) were higher in the faunated group. Differences, between groups, in proportions of VFA were attributed to the activity of the rumen bacteria rather than the ciliates per se.

7. No differences between groups were found in the concentrations of blood sugar and haemoglobin.

8. It was concluded that the changes due to the presence of rumen ciliates were not great enough to be reflected in animal performance under the conditions of this experiment.

1. Eighty bull calves, comprising forty-eight ayrshire and sixteen each of the Friesian and Jersey breeds, were used in a randomized block experiment. Forty calves were maintainted at a mean environmental temperature of 21° and forty at 14·5°. Within each temperature, twenty calves were reared from birth on a liquid milk substitute diet (pre-ruminant calves) and twenty were weaned at 35 d of age on to dry food (ruminant calves). Each type of diet was gien either ad lib. or at a restricted level. The calves were slaughtered at about 100 d of age.

2. The incidence of a high rectal temperature (> 39·39°) was greater for the pre-ruminant than for the ruminant calves during the first 14 d of life and throughout the whole experimental period, and was higher for calves at an enviromental temperature of 21° than for thosekept at 14·5°. During the experimental period as a whole, but not during the first 14 d of life, the incidence of diarrhoea was greater for the pre-ruminant calves. Mean rectal temperature was higher for the pre-ruminant calves and also higher for the calves reared at the high environmental temperature.

3. The incidence of lung lesions at slaughter was significantly higher in the ruminant than in the pre-ruminant calves, and tended to be higher at the high environmental temperature. There was a highly significant positive relationship between severity of lung lesions and incidence of a high rectal temperature (> 39·33°) and mean rectal temperature. Jersey and Friesian calves, but not Ayrshire calves, showed increased severity of lung lesions with increasing relative humidity at the low environmental temperature. When the results at the 'high' environmentaltemperature were combined with those obtained in an earlier experiment, the severity of lung lesiogs for Jersey and Friesian calves increased with decreasing relative humidity. At the ‘high’ but not at the ‘low’ temperature, severity of lung lesions was inversely related to skin weight/kgO·73.

4. Live-weight gain was much lower for the ruminant calves, but was unaffected by environ-mental temperature. Daily dry-matter intake from liquid diets given ad lib. did not differ be-tween breeds at the same live weight. In contrast, daily dry-matter intake from dry food given ad lib. was greatest for the Jersey and lowest for the Friesian at the same live weight. The same daily dry-matter intake from liquid as from dry diets was achieved at similar percentages of mature weight for the three breeds. Relative weight gain within type of diet was similar for Jersey and Ayrshire calves, but tended to be higher for the Friesian calves.

5. Carcassweight, carcass weight0·73, perirenal fat deposition, skin weight and killing out percentage were much lower for the ruminant calves. When adjusted for differences between treatment means for carcass weight0·73, perirenal fat deposition was greater at the ad lib. levels of intake and was 36% greater for pre-ruminant calves given milk substitute ad lib. at an environmental temperature of 21° than for those maintained at 14·5°.

6. It is concluded that there is no advantage to be gained from rearing calves at an environ mental temperature above 14·5°, unless increased fat deposition is required in veal calves.

1. Previous publications by the author and his colleagues have provided extensive records, and additional ruminating behaviour of cows receiving a wide range of diets. These recoreds, and additional unpublished records, have been used to justify a proposed index of the physical property of fibrousness, or roughage, in diets for ruminants.

2. It is proposed that the total time spent by ruminants in chewing their food, during eating and during ruminating, should be the basis of the basis of the roughage index

3. Experssion of the roughage index as total time spent chewing per kg dietary dry matter largely eliminates differences resulting from variation in the amount of food consumed, and differences resulting from the time of access to the food.

4. Examples of the proposed roughasge index are given. The values range from 145 to 191 min/Kg dry matter for oat straw ot under 20 min/kg dry matter for diets of concentrates or of finely ground herbages; hays and silages tend to fall in the region of 90–110 min/kg dry matter. Values for the indx increase with dietary proportaions of hay or straw.

1. Experiments in children and in animals seem to demonstrate that in marasmic malnutrition there is a reduction in the secretion of growth hormone. To study this problem the fasting, resting plasma concentrations of growth hormone were determined, before, and 45 and 60 min after, stimulation with an intravenous dose of arginine, in six infants with marasmus, in six infants with kwashiorkor and in five normal infants.

2. The values of plasma growth hormone (4·5 ± 0·97 ng/ml) in marasmic infants were significantly (P < 0·001) lower than those of the controls (7·8 ± 2·6 ng/ml), and responded little to stimulation with arginine (5·1 and 5·8 ng/ml at 45 and 60 min respectively), in contrast to those in the control group, which rose to 16·4 and 14·6 ng/ml. In children with kwashiorkor the values were very variable, but generally high, and showed little response (25·6 ± 13·3 before and 25·0 ± 17·6 and 14·2 ± 5·3 ng/ml at 45 and 60 min after stimulation respectively).

3. These results demonstrate that the responses of the hypophysis to deprivation of calories and protein (marasmus) and to protein deprivation (kwashiorkor) are different: in marasmus there is a progressive adaptation, with low secretion and poor reaction to stimulation, whereas in kwashiorkor the process is acute with high basal values of plasma growth hormone.

1. Experiments were done to find whether the rat liver can be maintained in a satisfactory condition when perfused with oxygenated Krebs-Ringer bicarbonate buffer without added protein or red cells.

2. The condition and preformance of the liver in this system were assessed from measurements made to ascertain its general condition or viability, its basal characteristics and its response to added substrates.

3. It was found that the rapid flow-rate of the medium through the livers and the efficient oxygenation of the medium ensured that enough oxygen was available for the livers to deal with large quantities of added lactate.

4. The potassium concentrations in the livers and the rates of alanine aminotransferase (EC 2.6.1.6) from the cells during perfusion, and the water content after perfusion showed that the livers were not grossly damaged and that they did not deteriorate measurably for up to 3 h of perfusion.

5. Liver oxygen consumption, ATP concentrations, lactate and pyruvate concentrations and ratios, and rates of urea and glucose synthesis and bile secretion, all in perfusions without added substrate, were either similar to measurements by other workers from livers perfused withmedia containingred cells and protein or were reasonable extrapolations from availabledata.

6. The rates of glucose production from lactate, and urea and glucose output from amino acids indicated that the liver responds adequately to added substrates.

7. Measurements of amino acid concentrations in perfusate indicated that the livers of rats starved for 18–20 h regulated the amino acids to characteristic levels, by overall output or uptake, except for valine, leucine and isoleucine which were continuously given out into the medium. The results suggest that in vivo there is a general flow of most of the amino acids from extrahepatic tissues to the liver during fasting, while valine, leucine and isoleucine flow from liver to extrahepatic tissues.

8. When pentobarbitone sodium (Nembutal) was used as the anaesthetic for removal of the liver from the donor rat, the rates of urea and glucose output in perfusions without added substrates were lower than when halothane (Fluothane) was used, indicating that pentobarbitone has an inhibitory effect on these measures of liver function during the subsequent perfusion.