From metabolism experiments carried out on the pigs enumerated in the first paper of this series the following conclusions are drawn:

(a) The metabolism in a state of inanition appears to be more a function of a power of the weight than of the true surface area as determined by the photographic method.

(b) Hogs born in the summer and autumn of one year appear to show two maxima of metabolism; one almost immediately, as has been observed previously, and another during the following summer, provisionally ascribed to the effect of light on thyroid activity, produced by the intermediary action of the anterior pituitary.

(c) Actual, and theoretically computed average growths are shown to agree remarkably well in the case of eleven of the pigs which were treated in an exactly similar manner. Individual growth curves showed no such agreement. This is considered to strengthen the evidence for the writer's previously stated view that nett energy is a statistical rather than a physiological constant.

1. It has been shown experimentally that the excretion of nitrogen noted by us in cultures of inoculated legumes takes place from the nodule bacteria, probably from the intranodular ones, and not from the roots. No excretion of amino acids occurs in cultures of uninoculated legumes growing on nitrate nitrogen.

2. Our earlier hypothesis that the legumes receive their nitrogen nutrition from the nodules in the form of organic nitrogen compounds, particularly amino acids, is in perfect accord with our new observations concerning the process of excretion. All facts indicate that the amino acids concerned are primary products of the nitrogen fixation, and not breakdown products of proteins. Bond's valuable work along quite different lines produced results which support this conclusion. He, however, did not study the chemical nature of the nitrogen compounds in question.

3. The excretion of nitrogen occurs in media capable of absorbing the excreted nitrogen compounds (cellulose, kaolin, sand, soil). The demonstration of the excretion is not possible in water cultures except when very large quantities of water are used. On the basis of these facts a hypothesis is advanced to explain the nature of the excretion.

4. The term total fixed nitrogen has been used as an expression for the extent of nitrogen fixation, while the term extent of excretion is employed to indicate that percentage of the total fixed nitrogen which is excreted from the nodules.

5. The extent of excretion depends largely on the strain used for inoculation. With strains of apparently equal effectiveness in nitrogen fixation, the extent of excretion may vary considerably, so that actually such strains differ in their effectiveness.

Composts on which the mushroom mycelium fails to make normal growth are a common cause of poor yields and crop failures. No investigation into the matter appears to have been made, though other aspects of mushroom nutrition have received attention. A good deal of research has been directed towards the discovery of the principal mineral (3, 5, 6, 7, 11) and organic (1, 2, 4, 6, 7, 8, 9) nutrients required by the mushroom. Environmental factors such as temperature (2), partial pressures of gases (12), concentration of soluble materials (6, 7), hydrogen-ion concentration (10, 11) and moisture content (7) of the compost have been studied. But failures occur, of the kind described, when these factors appear to be favourable and when the compost contains ample food material. It has been suggested (l, 2) that poor composts may be unsuitable in physical condition or contain injurious compounds. The influence of the physical or physicochemical condition of the compost on mycelial growth deserves attention, since a compost is a colloidal system composed of solid, liquid and gas phases. In such a system it is possible, without changing the chemical identity of the materials, to bring about great changes in free surface energy, kinetic energy, interfacial tensions, dispersion and hydration of colloids, electrokinetic phenomena, diffusion and osmotic pressures—all of which are probably of vital importance in the nutrition of the mushroom. The properties of stability, swelling and degree of dispersion of most colloidal systems are determined by the nature of the adsorbed ions, especially the adsorbed cations.

1. The effect of low-temperature grain pre-treatment on two winter varieties of wheat and two winter varieties of barley is seen in a very definite reduction in the number of tillers produced, which, however, had no subsequent effect on the number of ears surviving at harvest. Very little effect resulted from the treatment of spring varieties of wheat and barley in the number of tillers produced, although the spring wheat variety did show a slight reduction.

2. Gross yields per plot were unaffected by the treatment in all the varieties, but the yields per plant were affected in the wheat experiment, and the yield per ear in the barley experiment. There was a general increase in the yield per plant of all wheat varieties, while in the yield per ear one barley variety was unaffected, another showed an increase, while the third suffered a reduction.

3. The grain from treated plants was affected in 1000-grain weight and nitrogen content in the wheat experiment, while only the 1000-grain weight suffered any change in the barley experiment. Only one wheat variety showed an increase in 1000-grain weight, while each of the three varieties responded differently with regard to the nitrogen content of the grain. Similarly, each of the three barley varieties was affected differently with regard to 1000-grain weight, one being unaffected, another showing a decrease, while the third showed an increase.

4. Analysis of the behaviour of the varieties with regard to tillering and ear production showed clearly that the maximum of tillers produced bears little relation to the number of ears at harvest. In the barley varieties high yield and low nitrogen were associated with the largest number of ears, which in turn was associated with the lowest tillering. In the wheat varieties high yield was associated with high 1000-grain weight. In both experiments the spring varieties outyielded the winter varieties whether the latter had been treated or not.

Weights and measurements of sides of bacon made under standard conditions from different breeds and crosses of pigs and exhibited at the London Dairy Show from 1922–31 have been analysed statistically.

1. The actual live weight of the pig affects the carcass percentage more than does breed or type.

2. For a bacon pig of 200 lb. live weight, there is an optimum carcass percentage (about 79 per cent) and an optimum bacon percentage (about 58 per cent). The highest percentage is not necessarily best, for below about this level the proportion of bone will be too large and above this level the proportion of fat will be too large.

3. The reasons why certain measurements and proportions are necessary to meet market requirements are detailed.

4. The changes in the proportions of the side with increase in weight of the side are described. The proportional increase in bacon weight is much greater than the proportional increase in side length. Both belly thickness and thickness of shoulder fat increase in their proportions at a faster rate than side length, but not so fast as side weight. The thickness of fat over the loin is the only part measured which increases at a faster rate than side weight.

5. The subcutaneous layer of fat matures earliest at the shoulder, over the rump next, and on the loin last. The rate of increase of the back fat slows down as the sides increase in weight. This slackening of growth is greatest in the shoulder and least in the loin, the rump area being intermediate.

An account is given of methods which have been employed in laboratory and field studies of the actions of rolls on the soil. These studies have revealed little that is remarkable or unexpected concerning the actions of rolls on the soil, but they have clearly demonstrated that the exact actions of rolls differ widely according to the circumstances in which they are employed. When rolling is carried out in field experiments, it is necessary to perform tests to measure the exact effects produced on the soil. In this way it should gradually become more apparent when and how rolling is likely to be beneficial.

Of the methods which have been described, the last two, viz. tests of the consolidation, moisture content and tilth by means of a sampling tube, and of the mechanical resistance to the penetration of a probe with the automatic “resistance” recorder, are well adapted to use in field experiments. These methods are being used in many field experiments involving cultivations, and it is hoped that it may at some time in the future be possible by such methods to relate cultivations and crop yields through a knowledge of the soil structure.

Experiments have been conducted on heavy gault clay and on a gravelly loam to determine the effects of rolling and harrowing autumn-sown wheat in spring. It is concluded that rolling has no effect on yield on such soil types. In general, harrowing also had little effect on yield, although on three occasions it significantly increased the weight of grain per ear in excess of the increment to be expected from its effect on ear number.

The digestibility for poultry of a variety of huskless oats recently placed on the market has been investigated, and a comparison made with a widely grown variety of more usual fibre content.

It was shown that the fibre of the huskless oats was completely undigested, while that of the control variety had a digestibility coefficient of 8·8 per cent.

The digestibility of the crude protein in huskless oats was higher than in the variety Victory. It is suggested that this difference has resulted from the same cause as that which operates in ruminants, whereby fibre has a depressant effect on protein digestibility.

Both the organic matter and N-free extract were digested to a greater extent in the huskless oats than in the control variety. This is in keeping with the findings of other workers on the relation between fibre content and the digestibility of these constituents.

The composition, both organic and inorganic, and the digestibility of three grades of meat meal of widely differing fat content have been investigated. Large White hogs were used in the digestion trials.

The methods of manufacture of the meat meals have been described. They contained, on the basis of dry matter, 18·8, 11·1 and 3·2 per cent of fat respectively.

All three grades had a very high digestibility. The digestion coefficient of the main constituent, namely, the crude protein, ranged from 87·9 per cent in grade C (low fat) to 93·9 per cent in grade B (medium fat), these values comparing satisfactorily with the corresponding value for white fish meal, namely, 90·2 per cent.

The pigs digested the fat of the meat meals very efficiently. The fat of the grade A meat meal, forming 18·8 per cent of the dry matter, was digested to the extent of 95·4 per cent.

The grade B meat meal (medium fat) was the most digestible of the three grades tested. This is the grade that is marketed for feeding to livestock. The slightly lower digestibility of grade A (high fat) is attributed to the influence of the high fat content in causing a slight lowering of the extent to which the crude protein is digested.

The grade C meat meal (low fat) was produced from the grade B by “de-greasing” with petroleum benzine at 300° F. The results suggest that this process may result in a distinct lowering of the digestibility of the meal. The grade C meat meal is the most comparable with white fish meal in both digestible and mineral composition. In comparing the meat meals with white fish meal, however, it must be kept in mind that the former contain a much higher proportion of non-protein nitrogenous material.

1. It is shown that the leaf area: leaf weight ratio decreases with increasing leaf weight.

2. The relation between the leaf area: leaf weight ratio and leaf weight is well fitted by a linear regression equation.

3. A method of estimating the mean leaf area per leaf or per plant of a field crop by means of this regression is described. The mean weight per leaf is determined by a large sampling, and the leaf area: leaf weight ratio and its regression on leaf weight are estimated on a small subsidiary sample.

4. Alternative methods of estimation from the mean leaf weight and either the unweighted or the weighted mean leaf area: leaf weight ratio are shown to give positively biased estimates of mean leaf area.

5. It is emphasized that the small sample, from which the leaf area: leaf weight ratio and its regression on leaf weight are determined, must be a strictly random selection from the whole population.