The following is a réumé of a physical theory of soil moisture relations developed by the author in 1920 (1). On account of serious typographical and other errors in the original the essential argument is reproduced here together with some observations arising from subsequent work by other authorities.

A description is given of five typical soils of the Sudan covering a wide area. Of these, four are heavy clays and the fifth a sandy soil. All are alkaline and with one exception low in calcium carbonate. The results of the full chemical analysis of the conventional fractions are given and it is suggested that an important characteristic of a clay soil is the chemical composition of the clay fractions.

The carrying out of digestion experiments with swine introduces difficulties of technique which are not encountered in similar work with sheep. The pig is apt to be restive under restraint and does not always take kindly to the wearing of harness. The designing of a suitable harness is not easy on account of the shape of the pig, and when confined in a metabolism cage, the animal frequently spends much of its time rubbing vigorously against the sides, thereby considerably disarranging the harness. Moreover, since the pig increases in size so rapidly, it is necessary that the fit of the harness be capable of adjustment within wide limits. A further difficulty is connected with the voracious appetite and destructiveness of the pig, so that if the experimental ration does not satisfy the hunger of the animal, the latter will often gnaw the wooden parts of the crate and will even devour its own faeces, if the degree of freedom of movement permits it to turn round. The quantitative feeding of a pig is a matter of difficulty, owing to the animal's eagerness and its habit of stepping into the food trough. Swine do not display such hardiness under confinement as do sheep, and it is therefore necessary to maintain an equable temperature in the metabolism room throughout the experiments.

In calorimetric work the ideal experimental conditions are that all factors capable of influencing metabolism, except the one whose influence is the object of investigation, should be made constant or otherwise accounted for. It was while striving to attain such conditions that the necessity for this study arose.

During an investigation into the effect of food ingestion on the basal metabolism of the goat by the method of indirect calorimetry described by Orr and Magee(1) it was deemed inadvisable to ignore the diurnal variations in external temperature, and, consequently, it was decided to submit the animal to varying changes of external temperature and to determine their effect upon its basal metabolism. It was the special objective of the experiments to ascertain the critical temperature of the goat or the temperature at which the vital processes of the animal are most economically maintained.

The total metabolism of the pregnant goat remains at a steady rate from the 4th to the end of the 13th week of pregnancy. It increases steadily from the 14th to the 21st week, when a value is attained about 50 per cent, above the rate at the 14th week. Just before delivery the rate drops slightly. The increased metabolism is due partly to the increase in the mass of active protoplasm and partly to the stimulus exerted by the growing ovum on the maternal tissues. This stimulus tends to fall off slightly in intensity in early pregnancy and increases markedly in late pregnancy.

Post partum the total metabolism drops suddenly and continues to fall until the end of the 5th week; but the metabolism per unit of weight increases steadily until the 4th week and then declines. This increased activity of the maternal protoplasm is due to the processes of involution and repair.

In early pregnancy the increasing intra-abdominal pressure cuts short fermentation of food and causes the R.Q. to be higher in the pregnant than in the non-pregnant animal. As the pressure increases it begins to impede slightly the evacuation of the rumen so that the food ferments more thoroughly and the R.Q. falls slightly. After parturition the low intra-abdominal pressure aggravated by the laxity of the abdominal walls allows the food to remain longer in the rumen so that fermentation is more thorough and the R.Q. lower than in late pregnancy.

Two objectives were in view in undertaking this research.; to ascertain the cost in energy of muscular work in the goat and to investigate the adaptability of the Douglas-Haldane method of indirect calorimetry to work experiments on this animal. It is to the results of human experiments chiefly, that the present position of the physiology of muscular exercise is due which owes comparatively little to experiments on other animals. Zuntz and his school (1) have, however, compared the effect of a fixed amount of work on men, horses and dogs, and Lusk (2) has carried out some investigations into the influence of work on the dog. The principal obstacle hitherto in the way of employing animals other than man for work investigations has been the want of a sufficiently adaptable technique. Zuntz's experiments on the horse were conducted by means of a tracheal cannula, a device that, though fairly adaptable for work experiments, is not always desirable. Lusk's experiments were carried out in his respiration calorimeter where the applicability was very limited. Boothby and Sandiford(3) and Kunde(4) have carried out metabolic investigations on dogs by means of the Benedict apparatus, but here again the device is only of limited value for work experiments, which none of these workers have apparently yet undertaken. It was believed therefore that, if the proposed experiments were a success, in addition to possessing a certain physiological value, they would open up a wide field of research of great practical significance.

(1) Further experiments are described, the results of which support the relationship between the presence of vitamin A in the diet of the cow and its presence in milk fat.

(2) The typical winter ration of concentrates, roots and hay may be adequate to maintain the vitamin A value of the milk fat for considerable periods provided that at least one of the components supplies adequate amounts of that dietary principle. Well cured green meadow hays are in this respect greatly superior to dry brown seeds hays.

(3) The addition of cod liver oil to a winter ration deficient in vitamin A will induce a sharp rise in the vitamin A value of the milk fat of cows. No such effect is seen when oils deficient in this dietary factor (coconut oil, arachis oil) are given.

(4) The administration of cod liver oil in doses from 1 to 8 ozs. daily to milking cows caused no “fishy” taint in the milk or butter-fat.

(5) The administration of cod liver oil caused no appreciable change in the yield of milk but the higher doses appeared to cause a noticeable drop in the percentage of fat. Further experiments are required to throw more light on this observation.

A method for the determination of ammoniacal nitrogen in soils is described. It is an extension of the Hissink method for exchangeable bases to ammonium present in the soil. The working details are similar to the Hissink method, except that the leaching process is entirely carried out in the cold. The ammonia is distilled off with magnesium oxide.

Using normal sodium chloride as a leaching solution and collecting half a litre of leachings for distillation with magnesia, results were obtained which showed excellent agreement with those by the aeration method. Similar results were obtained using 250 c.c. of 15 per cent, sodium chloride solution, but the results are on an average about 1·6 per cent, lower. With high proportions of ammoniacal nitrogen a second half litre of normal sodium chloride leachings should be taken, or half a litre of 15 per cent, solution used.

The leaching method is economical of apparatus and water supply. It is therefore suitable for small laboratories with limited resources. It is fairly rapid: six estimations can be completed in a day.

The close agreement of the new method with the aeration method suggests that the amount of ammoniacal nitrogen in the soil at any given time is not an arbitrary quantity depending on conditions of estimation, but a definite amount. It is improbable that any ammonium compounds exist in the soil apart from those which take part in base exchange.

Various investigations on the decomposition of organic matter in the soil have brought out the fact that there exists a more or less constant ratio between the carbon and nitrogen content of the soil, whatever the ratio between these elements in the organic matter originally added to the soil. This ratio varies from 8: 1 to 12: 1, i.e. for every 8 to 12 parts of carbon, there exists in the soil one part of nitrogen; the average ratio is about 10 to 1. Brown and O'Neal (1923), for example, found that the ratio of the carbon to the nitrogen in a Carrington loam is 12: 1 to 13: 1, while, in the case of a Tama silt loam, the ratio may go down to 10: 1. According to Sievers (1923), the ratio of carbon to nitrogen in the soil is about 11·6: 1. Russell (1923) stated that, although there is about 40 times as much carbon as nitrogen in the original plant residues, the ratio will drop down to 10 to 1, before these residues have been very long in the soil. This ratio seemed to be in a stable position, for which no explanation could be suggested. Fraps (1922) found the ratio of carbon to nitrogen in the surface soil to be 9·2: 1 and in the subsoil 8·3: 1; he suggested, therefore, to judge the percentage of organic carbon in the soil from the percentage of nitrogen present.

The connection which has been shown to exist between the strength of wheat flour and the chemical individuality of the glutenine fraction of the wheat protein (Woodman, 1922) (1) led the writers to institute an enquiry into the manner in which the individual wheat proteins are developed and stored during the progress of the grain from the early stages after flowering to ripeness. The immediate object of the investigation was to secure information in regard to the stages at which the different proteins made their appearance in the grain and to determine at what point the character of the grain contents was such as to enable a tenacious gluten to be obtained by grinding up the kernels with successive quantities of dilute NaCl solution. It was also intended to follow the rate of alteration of the amounts of the several proteins during the growth of the grain and to attempt to elucidate as far as possible the relationships which exist between the simple and complex forms of nitrogen at the various stages.

Wheat owes its enormous importance to certain physical properties which are absent in the flours of other cereals, chief among which is the capacity of making a coherent dough on the addition of water.

Different wheats make loaves of different size and texture, a strong wheat being denned by Humphries and Biffen(1) as one which yields flour capable of making large well-piled loaves. From this definition it is seen that the conditions required of a strong flour are two, the first being that there must be a sufficiency of sugar or other materials available for fermentation and consequent production of gas in the dough, the second, that there must be some substance present in the flour which is capable of retaining a sufficiency of the gas so generated. The constituent of wheat flour in virtue of which its dough possesses this quantity of gas retaining power is the gluten. Many workers have attempted to explain strength in terms of the relative amounts of gliadin and glutenin in the gluten, or on the percentage of gliadin in the flour.

The effects of food ingestion on the total energy exchange of man and of the dog have been fairly completely worked out. Lavoisier was the first to show that the oxygen absorption and carbon dioxide production were increased by ingestion of food. Rubner, in addition to confirming these observations of Lavoisier, showed that the heat given off from the body after food was equal to the heat evolved from the foodstuffs actually oxidised within the body and thus established the agreement between direct and indirect calorimetry. He showed, further, that the increase in heat production was greatest after protein food. This specific effect of protein food he designated the “specific dynamic action.” The work of Rubner has been continued by, amongst others, Magnus-Levy, Benedict, and Lusk. The latter showed that the specific dynamic action of proteins is due to the special stimulating effect of certain amino-acids on the tissues and that the increased heat production after fat and carbohydrate ingestion is due to plethora of oxidisable molecules round the living body cells. Recently Wood and his school (1) have carried out investigations on the metabolism after food in pigs.

The post absorptive state commences in the ruminant between 42 and 48 hours after the last food. If food is ingested before this time it becomes mixed with that already in the rumen and its decomposition by fermentation is thereby accelerated. The metabolism at 15 hours after the last food is about 23 per cent, above that in the post absorptive state. For about 36 hours after th commencement of the post absorptive state the R.Q. remains below that of fat oxidation and fermentation gases still continue to be excreted. Keasons are suggested by way of explanation for these phenomena in the causation of which absorption of gas from the rumen does not appear to play any appreciable part.

1. The mechanical analysis of a number of soils, clays, and other granular materials has been carried out by the writer's method and the results have been set out in the form of curves showing the relationship between summation percentages and logarithm of settling velocity.

2. The curves obtained are smooth. This suggests that all the necessary information as to the mechanical composition of a material can be obtained by using a relatively small number of experimental points and drawing the appropriate curve. Results obtained on one scale can readily be transferred to another scale by interpolation.

3. The most common type of curve is a sigmoid. The steepest portion of the curve represents the fraction present in greatest frequency. This has been termed by the writer the modal fraction. Two sub-types were found. In the case of certain heavy clays, the modal fraction appears to be at the lower end of the curve, whilst in the case of materials mechanically disintegrated the modal fraction is at the upper limit of particle size.

4. Composite curves are obtained in certain cases. They may represent mixtures of different materials, or soils in the earlier stages of formation from rock.

5. The lower limit of particle size appears to be represented by log in the case of normal soils and clays. In the case of certain finely divided but non-plastic materials, the lower limit appears to be in the region of . It is suggested that a better picture of the properties of soils would be obtained by taking the limit for clay at this poiDt instead of at log .

6. The use of the logarithm of settling velocity as a measure of particle size is discussed and it is suggested that the use of negative logarithms might be avoided by using log (v × 107), for which the symbol Lv is proposed.

In the above I have shown the result of a series of measurements of the hydrion concentration in milk, cream, buttermilk and whey, partly employing Biilmann's Quinhydrone Electrode, partly Höber-Hasselbalch's Hydrogen Electrode.

The results of the tests agree.

Measurements have also been made in fresh and heated milk.

By these measurements I found no difference in the reaction or buffer action of the fresh and heated milk.

The Höber-Hasselblach method is rather slow. This is unfortunate as the reaction of the dairy products (especially whey) is apt to change when kept standing, even for a short time. By this method one also runs the risk of too high pH values owing to loss of carbon dioxide and it is therefore far from being an ideal one.

Biilmann's Quinhydrone Electrode is quick working, easy and simple and you avoid the above-mentioned sources of error. It is therefore to be preferred for measurements in the fluids in question. It is especially well adapted for titrations, as it makes possible a large number of measurements in a short time.