The results of a yield trial may be usefully indicative; they can never be decisive. Geographical differences of soil and climate and seasonal fluctuations, limit the applicability of results to the locality and the year of the experiment. No more can be achieved than to ensure that the data accumulated in the prescribed circumstances have as high as possible a degree- of statistical probability. For this, there must be adequate precautions against a variety of factors predisposing to error. These factors may be broadly classified as follows:

(a) Soil differences within the locality, i.e. major-scale differences as, for example, between the two ends of a 10-acre field.

(b) Soil differences within small portions of the test area, e.g. as between contiguous areas of 1 square ft. or even as between the areas occupied by neighbouring single plants.

(c) Differences in the seeds sown.

(d) Damage by wire-worm, etc., resulting in the killing off of some plants especially in the very early stages of growth.

(e) Irregularities in light intensity and inter-plant competition owing to irregular seed rate or depth of sowing, etc.

(f) Losses during harvesting.

(g) Irregularities in the water content of the harvested material.

1. Quantitative determinations have been made of the effect on soil protozoa and bacteria of various antiseptic substances, including benzene and its homologues and derivatives, carbon disulphide, ammonia, formaldehyde and chlorpicrin. Ammonia and nitrates were determined at the same time in many cases. The effect on fungi, eelworm, etc., was also determined roughly.

2. It was found that nearly all the substances disappeared from the soil fairly quickly and at the same time the numbers of bacteria fluctuated. The usual march of events was that the bacteria were reduced in number for the first few days, then rose to a maximum and finally fell slowly towards normal. The whole fall was sometimes very slow and the whole process was much slower in field soil than in the richer, lighter and better aerated greenhouse soils.

3. Aeration was found to have great influence on the rapidity of the changes.

4. The increase of the bacteria during the early days of an experiment varied in the same direction as the molecular weights and heats of combustion of the antiseptics and is attributed to the latter property. Naphthalene, for instance, which has a large heat of combustion, caused enormous rises, while benzene with its lower heat caused smaller rises.

5. This rise was independent of the effect of the substance on the protozoa. Both naphthalene and toluene in large doses cause high rises; the first has no effect on the protozoa, while the latter kills all amoebae and ciliates.

6. Similar results were obtained when the experiments were made on soils already free from protozoa, such as a field soil which had been in bottle for 76 years, soil in which they had been killed by steaming, and soil in which they had been killed by antiseptics. If the protozoa were killed by the use of a strong dose of a suitable antiseptic and the soil were then set aside for a long period, a second dose caused an even greater rise than the first.

7. It is therefore concluded that the rise in the number of the bacteria is largely due to the feeding effect of the antiseptic on the bacteria and not only to the destruction of the protozoa, and that the increased fertility observed by Russell and Hutchinson is to be attributed in large measure to the activity of the greater bacterial population in breaking down the organic matter of the soil. Bacterial rises following treatment with lime or steam are similarly caused in part by the preparation of the plant residues.

8. Aliphatic compounds cause quicker but smaller rises than those of aromatic series.

9. The introduction of a CH3 group into the benzene ring lessens toxicity to soil organisms, while a single Cl or nitro-group increases both toxicity and stability in the soil.

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.

Much work has been done in the past on the chemical composition of South African soils. The study of the physical properties of soils has, however, been somewhat neglected.

Transvaal soils differ from those of European countries in several important respects. In the first place, a large proportion of the soil is derived in situ from igneous rocks, and secondly, the country has never been glaciated in recent geological times. These two factors bear directly on the physical properties of the soils. Soil formation takes place chiefly by the chemical decomposition of rocks and only to a limited extent by mechanical disintegration. As a consequence we find in our soils very fine material, resulting from the chemical decomposition of easily weathered minerals, and rather coarse material which represents those rock constituents which are only subject in a limited degree to decomposition. In comparison with European soils particles of intermediate size do not play any dominant part in the mechanical make-up of Transvaal soils. Soils of alluvial origin are, of course, excepted. These latter occupy only a small area, but they are of considerable importance in the present stage of development of the country. Another factor which differentiates Transvaal soils from European ones is the presence in many of the former of finely divided hydrated ferric oxide. This feature will be discussed later.

1. An apparatus is described which has been designed to impart a known number of vibrations per minute to a suspension of soil or other material.

2. The problem of the calibration of the apparatus is briefly discussed.

3. A new method for the comparison of the mechanical composition of suspensions is described.

4. Various preliminary treatments of samples of soil for mechanical analysis are compared, and it is shown that:

(a) The rate of wetting is an important factor.

(b) A combination of triturition and vibration gives a satisfactory degree of dispersion.

(c) The use of acids is not advisable.

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 movement of water in soil, and the manner in which water is distributed over the particles and within the interstices, i.e. the dynamical and statical aspects respectively of moisture distribution, are of fundamental importance in soil science. The literature of the subject abounds with experimental determinations, but the difficulties of theoretical treatment are great, and it is only within recent years that any serious attempts have been made in this direction.

This investigation was undertaken in response to an enquiry respecting the value of lead nitrate as a source of nitrogen for manurial purposes. The ordinary commercial outlets for lead nitrate at the present time are in the manufacture of paper, printing ink and paint, also, in calico printing, where it is employed as a mordant. In the early stages of the War it was used as a shell-filling compound. Scrap lead is generally employed for its manufacture; a process which is protected by several patents. The trade in this commodity is relatively small.

1. Certain colloidal properties of winter wheat plants have been found to be closely related to frost resistance, and provide indices of hardiness which may have practical application in the breeding and selection of hardy varieties.

2. The imbibition pressure of fresh leaves, in the winter-hardened condition, was found to be in most cases directly related to hardiness.

3. The volume of press-juice obtained per 100 gm. of hardened leaves was inversely proportional to the hardiness of a variety. This volume is largely determined by two hardiness factors, the dry matter content and imbibition pressure of the leaves.

4. When unhardened leaves were used, no relation could be found between imbibition pressure or volume of press-juice and hardiness.

5. The imbibition pressure of hardened leaves appears to depend on the physical state of the cell colloids characteristic of living tissues, since this property was lost when the tissues were killed.

6. The moisture content of hardened tissues tends to be inversely proportional to hardiness. There is some evidence that in hardy varieties it fluctuates less with changes in weather conditions, and a possible explanation of this as a colloidal property is suggested.

7. The quantity of hydrophilic colloids contained in the press-juice, as measured by an effect on the activity of water, was found to be directly proportional to hardiness.

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.

The state of consolidation resulting from the nature and treatment of the previous crop has a most marked effect on the draft, causing variations from 107 to 580 lbs. in gross draft and from 68 to 483 lbs. in nett draft on a typical two-horse soil, the force exerted by each horse being about one hundredweight and a half.

The relation between draft and depth of furrow is linear, the nett draft per square inch tending to increase in value with increasing depth, except when the previous crop was roots, when a decrease at depths greater than 6-8 ins. is noticeable.

The relation between draft and width of furrow is linear, the nett draft per square inch in some cases showing an increase and in others a decrease with increasing width.

Considerations which are dealt with at length in Appendix III governed the form of the investigation upon tillering. In essence, the intention was to compare the pure lines P and A and to explore the possibilities of making accurate determinations of tillering. For reasons discussed in the Appendix, special steps were taken to secure for observation a population of plants which had had as great a uniformity of conditions as was attainable. The selection and sowing of the seed have been described in § I above. To promote further uniformity, plants of the following categories were excluded from observation: (i) all the plants of end rows; (ii) the end plants of all rows; (iii) plants which did not germinate on 26. iii. or 27. iii. (these days constituted the “modal” 2-day period of germination for the whole population); (iv) plants damaged to a noticeable degree by wire-worm or any other such agency; (v) plants whose immediate neighbour(s) in the row had died.

Single plot trials owing to the magnitude of the experimental errors, are practically useless as a test for comparing the yields of grain of one variety of oat with that of another. At best the results are only applicable to the particular experiment in question. For the old Scotch varieties of oat the probable error on trials of this kind amounts to about 18 per cent, of the yield of grain and to about 20 per cent, for the new varieties. Adopting single plot trials an 18 per cent, error means that when determining the superiority in the yield of grain of one variety over that of another and when the difference is not likely to be more than about 5 per cent, it would be necessary to have 214 centres with no duplication of plots at any centre in order to endeavour to obtain a conclusive result from a single year's trials. When the difference is likely to be about 10 per cent, it would be necessary to have 53 centres.

Data are supplied showing that the experimental error for different crops also for the grain and straw of the same crop is not the same. It is greatest for the grain and lowest for the hay crop.

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.

1. The coeruleo-molybdate method of Denigès affords a rapid means of estimating phosphates in such dilute solutions as are given by aqueous extracts of soils, 1:5, even when the extract is diluted twenty-fold.

2. High phosphate values were found for bog peats, but the majority of the soils studied gave to the extract phosphate corresponding to under two parts per million of phosphorus pentoxide. Dunged soil gave 20 p.p.m. or more.

3. Extraction for 3–4 hours gives values as high as extraction for 4–7 days with ordinary soils of low phosphate content, but the phosphate of richer soils may undergo a reversion to an insoluble form during prolonged extraction.

In recent communications accounts have been given of investigations which were designed to throw light on the nature and extent of the changes which occur when a green crop is converted into silage and to furnish information regarding the factors which influence the course of the fermentation and determine in a large measure the quality of the silage.

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.

1. The electrical conductivity of aqueous extracts of soils, in the proportion of one of soil to five of water, varies according to the time of extraction. In the more fertile soils extraction for three to four hours gives less than half as great a conductivity as is given in 4 to 11 days.

2. In peat the maximum value is reached almost at once, the extract having a high conductivity. The maximum value is also reached quickly in certain infertile soils, which give an extract of very low conductivity, closely similar to that of the purest upland streams.

3. A high electrical conductivity in the extract may only indicate the presence of an excess of salts, and does not necessarily indicate a good soil. It seems, however, that a rapid increase in conductivity as extraction is prolonged indicates increased solubility, partly through bacterial action and may be considered as a useful indication of fertility. A low conductivity, which remains low on continued extraction, denotes a soil so insoluble as to be unfertile.

In connection with nutritional investigations on poultry being carried out in the above Institute by the writer's colleague, Mr E. T. Halnan, it became necessary to devise a satisfactory method for the estimation of uric acid in poultry excreta. Although numerous exact methods have been elaborated for the determination of the amount of uric acid in mammalian urine, the corresponding problem in connection with the excreta of birds has received relatively little attention. This circumstance is no doubt due in large measure to the peculiar difficulty attaching to the quantitative investigation of the nitrogenous constituents of poultry excreta, arising from the fact that the urine and faeces are not excreted separately. The urine is not temporarily stored in a bladder, as with mammals, but proceeds directly from the kidneys through the ureters to the cloaca and there undergoes admixture with the faeces from the intestines.

Most of our information on the subject of vitamins has been derived from experiments on small animals fed on synthetic diets. The direct application of the results of such experiments to the feeding of farm animals under practical conditions is not warranted. Animals differ in the degree of their susceptibility to disease caused by lack of vitamins, and laboratory diets, composed of foodstuffs subject to abnormal physical or chemical processes, such as heating under pressure, or prolonged extraction with fat solvents, have no parallel in animal husbandry.