1. The effects of varying levels of physical activity were tested in rats, starting at ages of 21, 32 and 55 days and continuing until go, 100, 125 and 205 days.

2. Weight changes did not differ significantly between the exercise groups, except in the groups tested up to 205 days, when both the exercised group and the group with limited activity were significantly lighter than the control group.

3. The weight of the soleus muscle was significantly greater in the exercised rats compared with controls and rats with limited activity, except in the oldest age-group. The weight of the tibialis anticus muscle did not differ significantly between the different exercise regimes.

4. Heart weight was not significantly affected by the exercise regime, except that in rats studied from 55 to 125 days; the group with limited activity had significantly lighter hearts than those in the control group or the exercised group.

5. The percentage body fat was lower in the exercised group compared with the limited activity group, and was less than the control group in both the rats studied up to 205 days and those studied from 21 to 90 days.

6. Isoprenaline produced less cardiac damage in the exercised rats than in controls or in rats with limited activity. Animals who died following injection of isoprenaline had a higher percentage body fat than those animals with minimal cardiac damage.

1. The mean liver retinol reserve (retinal + retinyl esters, expressed as retinol) of six newborn lambs was 21±8 μg. The mean value for ten suckled lambs, aged 5–7 days, was 2655±472 μg retinol per liver.

2. Three unsuckled lambs were fed ad lib. from birth for 28 days on a high-protein diet, based on lard and skim milk, without supplementary vitamin A. The diet provided sufficient vitamin A for normal growth, but insufficient to permit substantial liver reserves (43±8 μg retinol per liver).

3. Thirty-six suckled lambs aged 5–7 days were given either a low-or a high-protein diet for 21 days, with or without graded levels of retinyl acetate or βcarotene. There were no significant differences in the live-weight gain or in liver retinol reserves between the low-and highprotein dietary treatments, or between the supplemented and unsupplemented groups.

4. Twelve lambs were pair-fed on either a low-or a high-protein diet from birth for 21 days. Six lambs that were given a large supplement of retinyl palmitate on the 1st day of life had stored significantly less retinol in the liver at 21 days (P > 0.01) than six lambs given a somewhat smaller total amount of retinyl palmitate in small daily doses. Lambs given the high-protein diet had significantly greater liver retinol reserves (P > 0.01) than lambs given the low-protein diet, with both methods of supplementation.

5. Twelve lambs were pair-fed from birth on a high-protein diet for 2 or 6 days. Lambs that were given retinyl palmitate dissolved in either a low-or a high-protein diet on the 1st day of life had significantly lower liver retinol reserves some 24 h later (P > 0.01) than lambs given similar treatments on the 5th day of life. Liver retinol reserves were positively correlated with the protein concentration of the diet at the time of supplementation.

6. Eighteen lambs were pair-fed from birth with either a low- or a high-protein diet. Six pairs were given retinyl palmitate daily and three pairs were given the supplement 48 h before slaughter. The source of protein was casein. Eight out of nine lambs given the low-protein diet would have died had they not been slaughtered at between 8 and 11 days of age. The time of supplementation had no significant effect on liver retinol reserves, which were very low, regardless of the dietary protein concentration. Lambs given the high-protein diet retained a significantly greater proportion (P > 0.05) of the dietary retinyl palmitate than lambs given the low-protein diet.

1. Thirty-four cross-bred newborn lambs were used. A high-protein diet (25% protein calories) was supplemented daily with retinyl palmitate (range, 13.75–440 μg/kg live weight 24 h), or with β-carotene (range, 68.5–2200 μg/kg live weight 24 h) for 21 days.

2. Live-weight gain was not increased by supplementing the basal diet with either retinyl palmitate or β-carotene.

3. The relative weights of β-carotene and retinyl palmitate (expressed as retinol) that were required to produce equivalent concentrations of retinol in the serum varied from 5:1 to 25:1, and for the liver (retinal + retinyl esters, expressed as retinol) the ratio varied from 3:1 to 9:1.

1. The action of vitamin D on the degree of mineralization of the bone tissue of rats given a diet containing adequate amounts of calcium and phosphorus for 8 weeks has been investigated by quantitative microradiography. The method is described.

2. There was a significant reduction in the growth of the vitamin D-deficient rats; the reduction was most marked in the females.

3. Serum analysis showed a reduction in Ca, but P was unchanged. However, the Ca × P product was considered to be high enough to permit normal mineralization.

4. The degree of mineralization of the cortical bone tissue increased significantly according to the distance from the epiphyseal plate. However, there were no significant differences between vitamin D-treated and vitamin D-deficient animals.

5. It is concluded that vitamin D deficiency in rats does not prevent the formation of a bone matrix which can attain a normal degree of mineralization.

1. Diets containing 1000 kcal/day with varying proportions of carbohydrate (CHO) were fed to four women with simple obesity. The patients were given, in various sequences and for 8 days in each instance, diets in which 3, 6, 12, 25 or 50% of the calories were supplied by sucrose.

2. No significant difference in the rate of weight loss was found when the diets of graded CHO content were fed and mean weight loss was 1.2 kg/week.

3. The high-CHO diets were antiketogenic; there was no daily relationship between urinary ketones and sodium. The 25 and 50% CHO diets had a nitrogen-sparing effect.

4. A 1000 kcal/day diet with about a third of the calories derived from CHO leads to a useful rate of weight loss and minimum changes in body chemistry. This finding may have implications in the long-term treatment of obesity.

1. Riboflavine given orally to sheep, calves, goats and ruminating kids gave rise, in milk and urine, to extra riboflavine accompanied by hydroxyethylflavine, by formylmethylflavine and by other as yet unidentified metabolites, but subcutaneous injection of riboflavine caused prolonged excretion of riboflavine in urine and milk unaccompanied by metabolites.

2. Placement of riboflavine by means of fistulas into the rumen, the abomasum or the caecum and abstraction of samples from the rumen or caecum showed that the rumen was the site of origin of the metabolites, thus accounting for the lapse of time of several hours between the ingestion of riboflavine and the appearance of hydroxyethylflavine in the urine and the absence of metabolites after subcutaneous injection of riboflavine.

3. Kids in which rumination had not yet become established could not produce metabolites from ingested riboflavine although, when fed milk containing the metabolites, they readily excreted them in their urine.

5. Incubation in vitro of kidney or liver tissue from cattle or goats with riboflavine did not give rise to metabolites, but these tissues could both reduce formylmethylflavine to hydroxyethylflavine in vitro.

6. Post-mortem examination of animals to which riboflavine had been fed showed the presence of metabolites only in gut contents, in the urinary bladder and in the bile. When injected, riboflavine reached the bile but no metabolites were produced.

7. Metabolites were found to occur naturally in the urine of ruminants in small amounts. Hydroxyethylflavine was readily demonstrable in the urine of the rabbit, but in the urine of the dog metabolites could not be found.

8. From these and earlier and later experiments the conclusion is drawn that riboflavine metabolites arise in the ruminant from the degradation of riboflavine by rumen bacteria.

1. Copper deficiency was induced in growing rabbits and the effects of ascorbic acid supplementation were studied.

2. Signs of Cu deficiency, including reduced growth, achromotrichia and alopecia, anaemia, and gross alterations in the bones of the forelimbs, developed most rapidly in those animals fed ascorbic acid.

3. Microscopic lesions in ossification centres were seen only in bones of rabbits which hadm received the vitamin.

4. Calcium and phosphorus contents of ash from cortical bone were not changed.

5. Compared with the controls, the concentration of liver Cu decreased and that of iron increased (> 50%) in Cu-deficient animals.

6. Cytochrome oxidase activity was reduced in liver and heart in Cu-deficient animals; this effect was accentuated in heart preparations from animals fed ascorbic acid.

1. The excretion of magnesium in urine, milk and faeces and of faecal dry matter (DM) by grazing monozygotic twin cows has been determined at intervals throughout four grazing seasons.

2. In Expt 1 three sets of twins were used to study the within-pair variance in the excretion of Mg and faecal DM. It was found that the variation within pairs was non-significant and small, less than 5% of the overall mean for all but one of the measurements made. The variation in urinary excretion of Mg within pairs was significant (P <0.05) in 1962.

3. In Expt 2 the effects of lactation on the excretion of Mg and faecal DM were studied. Only one of each of the monozygotic twins was in milk at a time, each twin being in milk for one season.

4. There were no significant differences in faecal nitrogen within and between pairs. On average, lactation increased faecal DM by 30% in 1964 and 24% in 1965.

5. The effect of lactation on urinary Mg was not consistent. For faecal Mg the effect of lactation was a simple reflection of the increased faecal DM since lactation had no effect on the concentration of Mg in the faeces. There was no correlation between the Mg excretion in urine and milk, either singly or together, with faecal Mg excretion.

6. The concentration of Mg in milk differed between twins and increased with length of lactation.

7. Mean intakes of Mg by the cows have been calculated from the values for the intake of DM and the Mg content of cut herbage and compared with total excretion of Mg in urine, milk and faeces. There was a significant correlation (P <0.05) between the sets of values but estimated intakes were lower (P <0.05) than excretions. The differences between intake and excretion differed between periods (P <0.001), being greatest between July and September. Selective grazing was considered to be the main factor responsible for these differences.

1. The excretion of calcium and potassium in urine, milk and faeces by grazing monozygotic twin cows has been determined at intervals throughout four grazing seasons.

2. In Expt I three sets of twins were used to study the variation within pairs in the excretion of Ca and K. It was found that the variation within pairs was non-significant and small, less than 5% of the overall mean, for all but one of the factors measured. The variation in urinary excretion of Ca within pairs was significant (P <0.05) in 1962.

3. In Expt 2 the effects of lactation on the excretion of Ca and K by three sets of twins were studied over two grazing seasons. Only one of each of the twins was in milk at a time, each twin being in milk for one season.

4. Lactation increased (P <0001) urinary and faecal Ca in 1964 but not in 1965. The concentrations of Cain the faeceswere lower (P <0.01) for lactatingthanfornon-lactating cows.

5. Lactation increased (P < 0.001) the excretion of K in urine and faeces. Differences within pairs in faecal concentration were significant in 1964 (P <0001) and 1965 (P < 0.01), but the effect was not attributable to lactation.

6. Significant differences between pairs were found for urinary Ca and K in 1964 (P < 0.05) and for the concentration of K in faeces in both years ( P < 001 or P < 0.001).

7. In 1964 greatest total excretions of Ca were found in June and July and of K in May, whereas in 1965, although the differences between periods for Ca and K were significant (P < 0.001), there were no obvious seasonal trends.

8. Mean intakes of Ca and K by the cows have been calculated from the estimated drymatter intake of herbage and the Ca and K content of the cut herbage and compared with total excretion in urine, milk and faeces. The differences between intake and excretion differed between periods (P < 0.001); for Ca, negative values were greatest in July and August in 1964 but not in 1965 and for K the values were small in July and large and positive in May, September and October in both years. The differences between lactating and non-lactating cows were significant for Ca(P < 0.001) and K (P < 0.01) in 1964. Selective grazing was considered to be the main factor responsible for these differences.

1. Hydroxyproline was determined in urine, carcass, and skin of young rats fed on low-protein and low-calorie diets.

2. Protein and calorie deprivation in young rats resulted in a marked fall in the soluble as well as insoluble collagen content of the skin.

3. The collagen content of the carcass (excluding skin) was slightly greater in the deficient rats than in the weanling rats, but very much lower than in the well-fed rats.

4. In rats subjected to protein and calorie deficiency, urinary hydroxyproline was markedly reduced. In these rats, most of the reduction in urinary hydroxyproline was observed within 1 week of feeding the deficient diet. Protein deficiency had affected urinary excretion of hydroxyproline more severely than calorie deficiency.

5. The reduction of urinary hydroxyproline in the deficient animals can be attributed to decreased turnover rate of their body collagen. This apparent decrease in turnover rate is explained as being due to an increase in the proportion of collagen of slow turnover in these animals.

6. Protein and calorie deficiency had also resulted in the depletion of non-collagen nitrogen of both carcass and skin.

1. Analyses have been made of milk collected from thirty wild African elephants immediately after they were shot.

2. The milk contained an average of 5.1% protein, 9.3% fat and 3.6% lactose. The concentration of lactose decreased and the concentration of protein and fat increased with advancing lactation. Inorganic constituents were present in approximately the same proportions as in bovine milk.

3. The contribution of capric acid to the total fatty acids, previously shown to be extremely high, increased with advancing lactation.

4. The significance of these findings to the preparation of a milk for rearing young elephants by hand is discussed.

1. Rumen bacteria were prepared in bulk from freshly killed sheep. They were exposed to ultrasonic disintegration and a preparation of cell walls was made by differential centrifugation.

2. The amino acid composition of acid hydrolysates of whole cells and cell walls was determined. Summation of these results shows that whole cells contained approximately 40% amino acids and cell walls approximately 30%.

3. A considerable proportion of the alanine content of cell walls was present as the D-isomer, partly ester linked as in teichoic acids and partly more tightly bound in ‘peptide linkage’ being released only after hydrolysis in constant boiling hydrochloric acid.

4. Cell walls were found to possess an alanine racemase which was inactivated only after incubation of the cell walls in 0.1 M-NaOH.

5. Whole cells contained approximately 8% carbohydrates and cell walls approximately 5%. The glucose and galactose contents of whole cells and cell walls were low, accounting for little more than 2% of the dry weight of the bacterial samples.

6. The amino sugar content of bacterial samples was approximately 3% and consisted mainly of glucosamine.

7. The total lipid content of rumen bacteria was approximately 25% and that of cell walls varied considerably between 10 and 23%.

1. Bacillus subtilis and Escherichia coli were grown on 14C-labelled glucose and used for the preparation of labelled whole cells, cell walls, cell contents and peptidoglycan.

2. The radioactive samples were injected into the abomasum of sheep and the 14C appearing in expired air, plasma glucose, urine and faeces was determined. Whole cells were also injected into the rumen and the incorporation of 14C into volatile fatty acids was measured.

3. All the bacterial preparations, including cell walls, were extensively digested and absorbed, Less than 15% of the radioactivity was recovered in the faeces.

4. Up to 20% of the radioactivity injected was recovered in expired carbon dioxide with only 2.4–8.1% passing through the glucose pool.

5. It has been calculated that under the conditions of the experiment 18.5 % of the total glucose entering the body pool of glucose in 24 h was derived from bacterial carbon.

1. Contents from the fermentative organs of the kangaroo and guinea-pig were found to have concentrations of total volatile fatty acids ranging from 50 to 140 mM.

2. In each instance acetic was the most abundant acid, followed by propionic, then n-butyric, Trace amounts of isobutyric, n-valeric and isovaleric acids were present.

3. When studiedin vitro, tissue from the wall of each fermentative organ was shown to metabolize butyrate to ketone bodies. Acetoacetate was the major ketone body. The presence of acetate and propionate did not affect ketogenesis from butyrate.

4. In the guinea-pig caecum most of the ketogenic activity resided in the mucosa.

5. The upper colon of the guinea-pig was as active as the caecum in metabolizing butyrate to ketone bodies.

6. For both the guinea-pig caecum and the kangaroo fermentative stomach, incubations with 14C-labelled butyrate showed that the proportion oxidized to CO2 was considerably less than that metabolized to ketone bodies.

1. Three heifers were changed from a diet of equal parts of hay and barley cubes (50:50 diet) to one entirely of barley cubes given in three equal feeds throughout the day. Feed intake was restricted to 80% of calculated appetite at the time of change and this percentage progressively decreased as the live weights of the animals increased.

2. The change of diet had no significant effect on the volume of rumen fluid but the rate of outflow from the rumen was significantly lower on the barley diet than on the 50:50 diet.

3. Animals on the restricted barley diet developed an exceptionally high rumen ciliate population and the bacterial population was shown by Gram films to include a number of organisms typical of roughage-fed animals. In culture, organisms of the genus Bacteroides were predominant but these appeared largely as cocco-bacilli in the Gram films. This microbial population was associated with a higher proportion of butyric acid than of propionic acid in the rumen fluid.

4. Occasional fluctuations in ciliate populations occurred in all three heifers. Decreases in ciliate number were paralleled by increases in propionic acid and decreases in butyric acid but not necessarily by a fall in pH. Under these conditions Gram films showed increases in bacteriodes-type rods and in certain curved Gram-negative rods.

5. Rumen ammonia concentrations were on average lower and showed a different diurnal pattern when ciliate numbers were reduced. Lactic acid concentrations were low and were not affected by the size of the ciliate population.

6. When the three heifers were given the barley diet ad lib. there was a decrease in rumen pH and a complete loss of rumen ciliates. The rumen bacterial population and the volatile fatty acid proportions were similar to those seen during decreases in ciliate number at the restricted level of intake. These changes also occurred in a fourth heifer which was changed fairly rapidly from the 50:50 diet to a restricted amount of the barley diet.

7. Two steers which had never had access to roughage were changed from ad lib. to restricted intake of the barley diet and were later given an inoculum of rumen ciliates. The rumen microbial population and the pattern of fermentation so produced were similar to those found in the heifers on the restricted barley diet.

8. Anomalous values were noted for total counts of rumen bacteria when free starch grains were present in the rumen fluid.

9. It is concluded that large ciliate populations and high proportions of butyric acid can be produced in animals fed exclusively on a barley diet by suitable adjustment of the intake and the method of feeding. It is postulated that the ciliate population may be largely responsible for the high butyric acid concentrations.

1. Short-term in vitro incubations of whole rumen contents have been used to measure the rate of production of volatile fatty acids (VFA) in two heifers given a diet containing 85% barley and 15% protein-mineral-vitamin supplement. Daily intake of the diet was restricted to 5.1 kg which was given in three equal feeds. In one heifer (no. 794), VFA production was measured over a 24 h feeding cycle; in the other (no. 832), a single 6 h feeding period was examined.

2. The feeding schedule outlined above was found in previous work to result in a major alteration in the rumen environment and in the end-products of rumen fermentation relative to findings in animals given the same diet ad lib. Some of these earlier observations have been confirmed and extended in the present work.

3. In heifer 794, the rate of VFA production reached a maximum (52–62 m-moles/l. h) 15 minafter each feed and then declined steadily throughout the remainder of the feeding period. Consistent changes with time were observed in rumen pH and in the concentration of VFA and dry matter in rumen contents during each feeding period.

4. Simultaneous measurements of rumen fluid volume and outflow allowed estimates to be made of VFA production and absorption in the entire rumen during each feeding period. In heifer 794, total VFA production amounted to 18.2 moles/day of which approximately 85 % was absorbed directly from the reticulo-rumen. On a caloric basis, total daily production accounted for 36. 5% of the digestible energy intake.

5. In heifer 832 there were significant differences in the rate of VFA production and in rumen pH and VFA concentration between two sets of observations made some 8 weeks apart. These differences appeared to be related to changes in the rumen microbial population and particular to a marked alteration in the numbers of ciliate protozoa. The possible role of rumen ciliates in modifying both the rate of VFA production and the environment within the rumen is discussed.

1. In each of three experiments, two sheep were given diets consisting of hay, or two parts hay to one part barley or one part hay to two parts barley. Each sheep was equipped with a cannula into the rumen and re-entrant cannulas into the proximal duodenum and the terminal ileum. The rations containing barley were supplemented to adjust the intake of calcium, phosphorus, magnesium, sodium and potassium to a level similar to that in the all-hay ration. Paper impregnated with chromic oxide (Cr2O3) was given twice daily by rumen fistula.

2. Amounts of crude ash and the five minerals entering and leaving the small intestine and excreted in the faeces were measured. The amounts passing through the re-entrant cannulas were adjusted to give 100% recovery of chromic oxide. The values were used to calculate the direction and net movements of the elements through the walls of the three main parts of the alimentary tract.

3. In all instances there was an extensive net secretion of Na and P between mouth and small intestine, net absorption of K and P from the small intestine and of Na from the large intestine.

4. The net movements of Ca and Mg were small and rather variable. In five of the six observations there was a small net secretion of Ca and small net absorption of Mg during passage of the digesta through the reticulo-rurnen, omasurn and abomasurn. Net secretion of Ca and Mg apparently occurred in the small intestine and net absorption of Mg in the large intestine.

5. The only between-diet differences were small differences in net movements of Na and K.