1. The retinol content of human liver tissue, obtained at autopsy from mortuaries in the London area, was determined in a group of 364 subjects.

2. Tissue samples from the central portion of the right lobe of the liver were saponified, extracted with light petroleum (b.p. 40–60°) and retinol assayed colorimetrically using the trifluoroacetic acid procedure.

3. The frequency distribution of retinol reserves was skewed to the right (positive skewness). The mean retinol content for the entire group was 252 mg/kg, with a median of 198 mg/kg and a range of 0–1201 mg/kg. Of the subjects, 49% had reserves in the range 100–300 mg/kg (regarded as the‘normal range’ for liver retinol) while 5% had reserves below 40 mg/kg (the arbitrary ‘cut-off’ point below which individuals are considered to be at risk). Only one subject had no detectable retinol reserves. On the other hand, 11 % of the subjects had reserves exceeding 500 mg/kg.

4. No sex-related differences were apparent, the median retinol reserves of male and female subjects being 190 and 202 mg/kg respectively.

5. Median retinol reserves varied markedly with age. They were relatively low (121 mg/kg) in infancy. but were approximately three times greater in childhood, adolescence and young adulthood. Thereafter, reserves declined gradually with increasing age to a low of 113 mg/kg in subjects over the age of 90 years.

6. When subjects were classified according to primary cause of death, the median reserves were as follows (mg/kg): accidental deaths 270, cancer 207, cardiovascular diseases 204, intestinal diseases 178, nervous diseases 164, hepatic diseases 158, respiratory diseases 141, sudden infant death syndrome 127.

7. Retinol reserves in London are substantially higher than those reported from North America and are exceeded only by those reported from New Zealand and Ghana. It is therefore concluded, from the results of this survey and also from official estimates of the dietary intake of retinol and provitamin A carotenoids, that vitamin A status in London, and probably also in the rest of Britain, is quite satisfactory.

1. The energy metabolism of ad lib.-fed adult male Wistar rats receiving daily running exercise (0·9 km/d; 8° incline) on a motor-driven treadmill, over a period of 56 d, was compared with that of sedentary ad lib.-fed rats and sedentary restricted-fed rats of similar body-weight (approximately 420 g).

2. The metabolizable energy of the diet (Oxoid 41B) was 11·44 ± 0·05 kJ/g. This value was not affected by restricted feeding (70% ad lib.), exercise training or exercise itself.

3. Exercise-trained rats ate 5% more food than the sedentary ad lib.-fed rats but their equilibrium body-weight was 60 g lower than that of the latter group.

4. Resting metabolic rate, measured over 22 h in a respiration chamber was increased by 10% in exercise-trained animals.

5. Feeding increased energy expenditure (dietary-induced thermogenesis) and this effect was potentiated by performance of an exercise task.

6. Exercise-trained rats exhibited anticipatory rises in energy expenditure (approximately 40%) when placed on a stationary treadmill.

7. Treadmill work increased energy expenditure by a factor of 1·9–2·4.

8. The energy cost of the exercise, determined by respiration calorimetry was 66–80 J/g per km. These energy costs did not account for all the differences observed in food energy consumption of exercise-trained and sedentary rats of equal body-weight.

9. It is concluded that regular physical exercise increases energy expenditure by factors additional to the energy requirement directly related to the physical work. These factors include an increased resting metabolic rale in exercise-trained rats, increased dietary thermogenesis induced by exercise and anticipatory increases in energy metabolism during the period preceding exercise.

1. The response of Lactobacillus casei was measured for a number of the monoglutamyl forms of folate derivatives.

2. At the concentrations of folate commonly used in the assay of folate vitamin in foods the response of L. casei to folic acid, (pteroyl glutamic acid) and 5-formyl-tetrahydrofolic acid was similar, but 5-methyl-tetrahydrofolic acid gave as little as half the response of folic acid.

3. The response was modified by altering pH but not by concentration of ascorbate.

4. These results have implications for the assays of foods for folate where mixtures of folate derivatives are present.

5. A modified procedure is suggested in which the monoglutamates give similar responses.

1. Studies were made on the lysine content of casein reacted with caffeic acid oxidized aerobically under alkaline conditions or enzymically with tyrosinase (EC 1.14.18.1).

2. Loss of fluorodinitrobenzene (FDNB)-reactive lysine was rapid at pH 10 and increased with time and the temperature of the reaction, with concentration of caffeic acid and with the oxygenation of the mixture. In presence of the enzyme mushroom tyrosinase, maximum reduction of reactive lysine occurred at pH 7 and was dependent on the reaction time and on the concentration of caffeic acid.

3. Reaction of α-formyl-L-[U- 14C]lysine with caffeic acid at pH 10 showed the rapid formation of five reaction products which appeared to polymerize gradually as the reaction progressed.

4. The nutritionally available lysine content of the casein-caffeic acid mixtures, as assayed with rats, was reduced after both alkaline and enzymic reactions, as were faecal digestibility, net protein ratio and net protein utilization. Biological value however was not reduced.

5. In metabolic studies using goat milk casein labelled with L-[3H]lysine and reacted with caffeic acid in the same way, the lysine–caffeoquinone reaction products were not absorbed by the rat but were excreted directly in the faeces.

6. The importance of the reaction of proteins with caffeoquinone and chlorogenoquinone (formed by the oxidation of caffeic and chlorogenic acids respectively) is discussed in relation to the production of sunflower protein, leaf protein and other vegetable-protein concentrates.

1. Two groups, each of six rabbits, were fed on semi-purified diets containing either 400 g casein or 400 g soya-bean protein/kg for 20 d and then the diets of the two groups were crossed-over.

2. Just before the cross-over, the serum cholesterol concentration (mean ± SE) was 3068 ± 592 and 800 ± 143 mg/l for the groups fed on casein and soya-bean protein respectively.

3. Changes in the serum cholesterol concentration were observed 1 d after crossing-over the diets. By 10 d, the cholesterol levels in the two groups had also crossed-over.

4. The changes in serum cholesterol level after the cross-over were reflected in the very-low-density lipoproteins (VLDL) and low-density lipoproteins (LDL).

5. Lipoprotein protein concentrations in the LDL changed in the same way as cholesterol. In the VLDL however, the protein concentration decreased in both groups after the change in diet.

6. The cholesterol:protein values for the LDL and VLDL markedly increased in the rabbits changed from the soya-bean-protein diet to the casein diet, reaching a maximum 2 d after the cross-over. In the animals switched from casein to soya-bean protein, the values progressively declined.

7. The source of dietary protein exerts a rapid effect on the composition of both the VLDL and LDL which is proposed to be attributed to changes in the number and size of lipoprotein particles.

1. The phospholipid intake by eight healthy women was studied by the duplicate-portiontechnique, i.e. chemical analyses of duplicates of the food consumed. Their intake of phospholipids was 1·5–2·5 mmol lipid-phosphorus/d, which correspondsto 0·023–0·059 mmol lipid-P/g dietary fat and 0·24–0·45 mmol lipid-P/MJ respectively.

2. Choline phosphoglyceride constituted 480–700 mmol/mol and ethanolamine phosphoglyceride 170–240 mmol/mol total lipid-P. Most of the choline in nature occurs as choline phospholipids, the intake of which ranged between 0·91–1·85 mmol/d or 0·15–0·33 mmol/MJ.

3. Palmitate, stearate, oleate, and linoleate were the four major fatty acids both in choline phosphoglyceride and ethanolamine phosphoglyceride. Significant amounts of highly unsaturated, C20 and C22 fatty acids were also observed. It was calculated that 13–33 mg/g total dietary fatty acids was consumed as phospholipids. Together with bile phospholipids, dietary phospholipids and their degradation products may be important in the digestion and absorption processes.

1. Basal levels of serum 25-hydroxy vitamin D (25-OHD) were estimated in ten normal children and twenty-seven children with protein–energy malnutrition.

2. Five normal children and fourteen malnourished children were administered a single massive dose of 15 mg vitamin D orally and the remaining children received oral supplements of 50 μg vitamin D daily for 20 d. Blood samples were obtained after 10 and 20 d of dosing and serum 25-OHD levels were repeated.

3. The basal serum 25-OHD levels were significantly lower (P < 0·05) in malnourished children than in normal children.

4. Administration of a single massive dose of vitamin D as well as daily supplementation of small doses resulted in significant increases in serum 25-OHD levels within 10 d. However, the increase with a massive dose was of a higher magnitude. There was no significant difference between the normal and malnourished children.

5. The binding capacity of serum to 25-OHD was similar in both the groups.

6. These results suggest that vitamin D metabolism is not altered in protein–energy malnutrition.

1. The concentrations of vitreous humour and plasma glucose were closely correlated in both healthy and fatty liver and kidney syndrome-affected chicks at time of death.

2. The values of vitreous humour glucose and lactate decreased rapidly after death, such that they were not reliable indicators of the presence of hypoglycaemia immediately ante mortem.

3. Hepatic glycogen was extremely low in fatty liver and kidney syndrome-affected birds, whereas significant quantities remained in healthy birds up to at least 24 hpost mortem.

1. Iron absorption was studied in weanling rats using balance techniques from semi-synthetic diets containing dried white bread (60·5 g dietary fibre/kg, White & Southgate, unpublished results), brown bread (130·2 g dietary fibre/kg) or wholemeal bread (221·2 g dietary fibre/kg) at a level of 300 g/kg and compared with a control group given a diet containing added FeSO4 at a similar Fe level to that for the bread groups. The dried bread contained 6·2–6·4 g phytate/kg.

2. Absorption of Fe was significantly higher (P < 0·001) in the control group (0·45) than in the white (0·28), brown (0·31) or wholemeal (0·24) groups.

3. A second experiment was carried out on 6-week-old rats in which the dried bread was extrinsically labelled with 59Fe and absorption from a single meal measured by both faecal excretion and incorporation of 59Fe into the blood. Control animals were given 59FeSO4 for comparison.

4. The excretion of 59Fe (% of administered dose) was significantly lower (P < 0·001) in the control group (31) than in the white (48), brown (45) or wholemeal (47) groups. After 10 d the control group had significantly more 59Fe in the blood than the bread groups, but there were no differences between the bread groups.

5. It appears that wheat bran fibre itself has no effect on the retention of Fe from the diet in the rat, when supplied in amounts similar to those found in commercially-available bread.

1. Whole-body retention in vivo and uptake of 59Fe-labelled ascorbate and nitrilotriacetate chelates by intestinal slices in vitro were determined in groups of normal control rabbits and rabbits with experimentally-induced Fe deficiency.

2. Over-all absorption as measured by retention of doses of either chelate was greatly increased in conditions of Fe deficiency.

3. Intestinal Fe uptake in vitro was inhibited up to 77% in the presence of 2,4-dinitrophenol and sodium fluoride. Initial rates showed saturation within the concentration range 18–450 μmol/l, suggesting that uptake was brought about by an active transport process.

4. When studied at chelate concentrations of 450 μmol/l, significant regional differences in uptake rates were observed. Uptake in duodenal slices was increased when compared with slices from jejunum and ileum.

5. Fe uptake from ferric and ferrous chelates was greatly enhanced in Fe deficiency. This was chiefly due to increases in uptake by slices from the duodenum, but uptake into slices of distal intestine was also stimulated.

6. Kinetic analysis of Fe uptake by duodenal slices from animals rendered Fe deficient by diet or repeated bleeding indicated in both groups an increased apparent maximum velocity (Vmax) for influx of Fe without significant changes in apparent affinity for Fe.

7. The experiments provide further insight into the nature and regional distribution of transport of Fe into the intestine and suggest, in the rabbit, that important control of Fe absorption may be exerted by an active process operating at this initial entry step.

1. The effects of two isoenergetic diets differing only in the values for polyunsaturated: saturated fat (P : S values of 0·2 v. 2·0) were studied in twenty adult human volunteers.

2. A period of 14 d on the high P:S diet failed to produce significant changes in fasting triglyceride levels, though there were individual variations. On the other hand, fasting cholesterol levels dropped by 10% (P < 0.005). High-density-lipoprotein-cholesterol concentrations were not influenced by changes in the P:S value.

3. Investigations into the mechanism by which changes in the P:S value might affect plasma triglyceride values revealed no consistent effects on very-low-density-lipoprotein kinetics, insulin secretion, insulin sensitivity or free fatty acid concentrations.

4. The results of this study suggest that the largest increase in dietary P:S values that is likely to be obtained on a long-term basis may have only a small effect on plasma triglyceride and cholesterol concentration.

1. The abilities of cattle, sheep, goats, equines and rabbits to digest mature timothy (Phleum pratense) hay were compared. Apparent digestibilities were partitioned into true digestibility, metabolic faecal output (MFO) and fibre digestibility. The aim of the study was to determine the relative effects of fermentation site (among groups) and of body-weight (within groups) on the efficiency of digestion.

2. The ruminants were superior to equines, which were in turn superior to rabbits, in digesting fibre components of the hay. A large individual variation in digestibility was noted only for the equines. Increasing body-weight was associated with higher digestibility in ruminants, but no such trends were seen in the non-ruminants.

3. The MFO expressed as a proportion of dry matter intake gave similar values for all groups (0·085–0·118). As a proportion of available microbial substrate originating from the feed, the values were found to be 0·167 for the ruminant, 0·425 for the equines and 2·13 for the rabbits. The value for the rabbits shows that their lower tract microflora must obtain energy from non-fibre components of the feed. No appreciable digestion of the generated microbes by the host was suggested by the values obtained for the equines.

1. Serum and intracellular distribution of retinol was determined in equines maintained on four levels of vitamin A intake.

2. The form of retinol transported in serum was determined by gel filtration and chromatography to be a complex of retinol bound to a protein of molecular weight (MW) of approximately 20000, which was in turn complexed probably with prealbumin to yield a complex with a MW of 75000 to 80000.

3. Increasing dietary vitamin A levels enhanced the concentration of lipoprotein-bound retinyl esters in the plasma.

4. Vitamin A in the liver cytosol was found predominantly as retinyl esters in a lipid–protein aggregate of MW approximately 2 × 106 and hydrated density of 1·063–1·111. In the kidney and adrenal gland, two Iipid–protein entitites were found with MW of approximately 1·8 × 106 and 1·7 × 105 respectively. These fractions contained approximately 40 and 20% lipid respectively and had densities of 1·063–1·111 and approximately 1·21.

5. All lipid–protein aggregates were associated with retinyl palmitate hydrolase activity and guanidine treatment released a 15000 MW material, presumably intracellular retinol-binding protein.

6. Increasing dietary vitamin A enhanced the proportion of retinol in the 1·7 × 105 fraction.

7. Findings in equine plasma and liver resemble previous observations in other species. The characterization of two new lipid–protein aggregates in equine kidney and adrenal glands, which have hydrolase activity, may be important in intracellular retinol transport and metabolism, especially in animals subjected to high intakes of vitamin A.

1. Raw soya-bean meal (RS) was fractionated into soya-bean lyophilized extract (SLE), soya-bean lyophilized residue (SLR), acid-precipitated proteins (APP) and whey proteins.

2. Trypsin (EC 3.4.21.4) and chymotrypsin (EC 3.4.21.1) inhibitors (TI) were soluble at pH 8 and remained soluble after the extract was acidified to pH 4·4. Except for whey, heating abolished, almost totally, their inhibiting activity.

3. Feeding SLE diet (high TI content) and APP diet (low TI content) resulted in growth depression below the RS level. Feeding the SLR diet resulted in an optimal growth. Feeding diets containing heated fractions improved the growth rate though not to the level observed with heated RS (HS) diet.

4. RS, SLE, APP and whey diets produced similar pancreatic enlargement which could be totally (RS, whey) or partially (SLE, APP) abolished by heating.

5. Feeding the RS diet reduced pancreatic amylase content. The factor responsible for this effect cofractionated with SLE and whey proteins.

6. Two groups of factors in the various diets were probably responsible for the elevation in pancreatic proteases. The first group were the heat-labile factors present in RS, SLE and whey whereas the second group resisted the heat treatment and were found in APP and SLR.

7. The results suggest that for optimal growth rate of rats, heat treatment should be given to the unfractionated soya-bean proteins rather than to the isolated fractions. The results further indicated that TI are not the only factors that can lead to pancreatic enlargement and changes in pancreatic enzymes composition.

1. Fermentation and absorption of constituents of digesta in segments of the large intestine of sheep given different diets were studied by analysis of gut contents obtained at slaughter after a period during which the sheep had been administered a non-absorbable gut marker.

2. In sheep given chopped, dried lucerne (Medicago sativa) there was net absorption of water throughout the large intestine with concomitant increases in the proportion of dry matter (DM) And organic matter (OM). There was net disappearance of 62 g OM, 1·66 g non-urea non-ammonia-nitrogen (NU–NAN) and 0·6 g(urea + NH3)-N in the caecum and proximal colon. There was no significant change in OM and NU–NAN flow through the remainder of the large intestine but there was a net disappearance of 0·3 g NH3–N. There was also net appearance of volatile fatty acids (VFA) in the caecum, most of which was apparently absorbed before the rectum.

3. Metabolism in the caecum was also studied in sheep grazing fresh pasture or consuming one of three sugar cane-bagasse-based diets, or barley pellets. In the lucerne- and pasture-fed sheep there was a net disappearance of approximately 0·5 g NH3-N/d from the caecum, while in sheep fed on bagasse plus urea, 1·4 g NH3-N/d was apparently absorbed from this region. The addition of fish meal to this latter diet resulted in apparent disappearance of 5·3 g NH3-N/d from the caecum and proximal colon.

4. There was apparent loss of NU–NAN from the caecum of sheep on all diets except the barley diet. With the latter diet there was a net gain of 1 g NU–NAN/d which was associated with relatively high VFA concentration and production; taken together these results indicate that microbial fermentation in the caecum was more extensive in the sheep fed on the barley diet than in those fed on the other diets.

5. The proportions of individual VFA in digesta from the rumen and caecum of lucerne-fed and pasture-fed sheep and in digesta from the caecum of sheep given the bagasse-based or barley diets are also reported and discussed.

6. In general the results indicate that the caecum and to a lesser extent the proximal colon were the major regions of fermentation and absorption of the components of the digesta in the large intestine.

1. Experiments were undertaken to examine the errors associated with the use of indigestible markers, the 51Cr-labelled complex of chromium ethylenediaminetetra-acetic acid (51Cr-EDTA) and 103Ru-labelled tris-(1,10-phenanthroline)-ruthenium(II) chloride (103Ru-P), to measure liquid- and solid-phase digesta kinetics in the caecum and proximal colon of sheep.

2. First-order kinetics of markers were observed following either single injection or termination of continuous infusion. There were no differences between the half-times (T½) of marker in the caecum plus proximal colon whether calculated from marker concentration in caecal digesta or in faeces. There were also no differences in the T½ values calculated for the liquid- and solid-phase markers. When pool sizes calculated from the marker kinetics were compared with the volume of digesta present in the caecum and proximal colon at slaughter, it appeared that the 51Cr-EDTA and 103Ru-P caecal pools described the digesta contained in the entire caecum and proximal colon.

3. The flow-rates of dry matter (DM) through the caecum of sheep given 694 g lucerne (Medicago sativa) DM/d were similar whether estimated from total collection of faeces, by single injection of marker, or by the ratio, marker concentration: DM in either caecal digesta or faeces during continuous infusion of marker into either the rumen or the caecum.

4. In sheep given 553 g brome grass (Bromus inermus) DM/d the coefficient of variation of estimates of the plateau of 51Cr-EDTA marker during continuous infusion into the caecum was greater when 130 ml infusate/d were administered than with 1000 ml/d.

5. In the sheep given brome grass the lines of best fit of decline in In 51Cr-EDTA marker concentration v. time following termination of the continuous infusions described previously and following single injection of marker in 20 or 2 ml into the caecum were examined. The variation was least when 1000 ml infusate/d had been administered and was unacceptably large following a single injection of 2 ml.

6. These experiments showed that tracer techniques could provide unbiased estimates of trace kinetics in the caecum and proximal colon.

1. An immunochemical test for predicting the suitability of different soya-bean products for feeding to preruminant calves was studied. Calves fitted with abomasal and re-entrant ileal cannulas, were first given a series of feeds containing heated soya-bean flour and two with casein as the protein source, and then given further test feeds in which different experimental soya-bean products, prepared under conditions which might be used commercially, provided the nitrogren source. These products (Q, R, S and T) were prepared respectively by extracting fat-free soya-bean flour with aqueous ethanol at 960, 650, 650 and 550 ml/l and at 60, 60, 78 and 78° and then treating the residue with steam for 30 min.

2. After infusion of a test feed into the abmasum measurements were made of transit time through the small intestine, flow-rate of ileal digesta, recovery of polyethylene glycol (a water-soluble marker added to the feed) and net N absorption up to the distal ileum. Glycinin and β-conglycinin, antigenic constituents of soya-bean protein, were determined in saline (9 g sodium chloride/l) extracts of soya-bean products by haemagglutination inhibition assay.

3. After calves had been given a series of four feeds containing heated soya-bean flour, they showed hypersensitivity to the flour by developing disturbances in digesta movement and N uptake. When experiments were made to compare the effects of giving feeds based on casein with those containing products R, S and T it was shown that some differences in transit times and flow-rates of digesta through, and N absorption from, the small intestine occurred. Disturbances were, however, much less than those observed with product Q feeds.

4. Haemaggultination inhibition assay of products Q, R, S and T gave titres (log2 reciprocal of highest dilution of saline extract inhibiting agglutination) of 12, 5, 3 and 2 for glycinin and 13, 3, 3 and 2 for β-conglycinin respectively. After steam treatment only product Q gave measurable titres; 10 and 11 for glycinin and β-conglycinin respectively.

5. It is concluded that the haemagglutination inhibition assay is a suitable in vitro method of indicating whether soya-bean products given in liquid feeds to preruminant calves will cause gastrointestinal allergic reactions. Furthermore, results show that the removal of deleterious factors from soya-bean meal by treating with ethanol, is critically dependent on the proportion of water present in the ethanol and the temperature of the treatment.

1. Glucose metabolism and changes in the concentrations of several hormones in jugular plasma were measured in growing lambs fed on fresh pasture ad lib. One group of lambs acted as control while the second received a continuous abomasal infusion supplying 44 g sodium caseinate + 0·5 g L-methionine/d.

2. Hormone concentrations were determined by radioimmunoassay procedures and glucose irreversible loss measured from continuous infusion of D-[U–14C]glucose.

3. Protein infusion increased plasma concentrations of insulin, glucagon and thyroxine (T4), depressed those of growth hormone, prolactin and somatostatin and had no effect on triiodothyronine (T3) concentrations. Cortisol concentrations also tended to be slightly higher in the plasma of protein-infused lambs.

4. Increases in herbage intake within the ad lib. range were associated with increases in plasma insulin and glucagon concentrations and decreases in growth hormone concentration, and it is suggested that these effects could be mediated in part by the accompanying increases in protein absorption from the intestines. The T4:T3 value also decreased with increasing herbage intake, and it is suggested this was due to conversion of T4 to T3.

5. After correction by covariance to equal herbage intake, rates of irreversible glucose loss for control and protein-infused lambs were 9·2 and 10·0 mg/min per kg body-weight0·75. It was calculated that respectively 0·12 and 0·19 of the total glucose production in control and protein-infused lambs could be accounted for by net synthesis from protein.

6. It was concluded that changes in the circulating concentration of several hormones in protein-infused compared with control lambs were likely to have been implicated in protein deposition forming a greater proportion of energy retention in the infused lambs (0·41 v. 0·27).

1. The Rumen Simulation Technique (Rusitec) was used in a series of long-term experiments to study the distribution and changes of urease (EC 3.5.1.5) activity in a heterogeneous fermentation system.

2. It was shown that in Rusitec the high urease activity from the inoculum decreased to low values, that the rate of decrease was consistent with simple dilution of ureolytic micro-organisms and that the urease activity could be restored to original values by infusion of urea into the reaction vessels. The magnitude of this urease activity was a direct function of the amounts of urea infused. Single daily additions of the same or greater amounts of urea in food or as solid failed to increase the urease activity significantly.

3. In general, urease activity increased 2–6 h after feeding and the increases were greater with roughage diets.

4. The ureolytic activity per unit volume was always higher in compartment 2 (space occupied by micro-organisms that are loosely associated with the solid) than in compartment 1 (strained rumen contents) or compartment 3 (space occupied by microbial population that cannot be washed out of the solid matrix).

5. The distribution of urease activity between the compartments was different from the distribution of certain other enzymes (e.g. protease and alkaline phosphatase (EC 3.1.3.1)).

6. Apart from the boundary region, the concentrations of urease, ammonia and volatile fatty acids in compartment 2 were constant, while the concentrations of protein, DNA and another enzyme (alkaline phosphatase) increased with the depth of the compartment. Specific urease activity (per unit weight of protein or DNA) was much higher in compartment 1 than in compartment 2 and it decreased markedly with depth of compartment.

7. The concentrations of ammonia were always much higher in the solid matrix (compartments 2 and 3) than in the free suspension of micro-organisms (compartment 1). There was a linear relation between these two quantities.

8. The results are discussed in relation to published work on the entry and metabolism of urea in the rumen.