In a previous paper (1) some of the factors which control fertility in domestic animals were discussed. These for purposes of clearness in investigation were divided into two groups: (1) The factors which control the number of eggs shed; and (2) The factors which control the number of eggs which develop to reach birth size. By this means the way in which the various factors which affect fertility could be determined, for example, it was shown that the effect of age on fertility, the literature of which has been reviewed by Harris (2), is due to the number of eggs shed at each oestrus period. Young sows examined had on the average 14 corpora lutea in the ovaries while old sows had 20 corpora lutea.

Records of the live and carcase weights of sheep exhibited at the Smithfield Show from 1893 to 1913 have been treated statistically. The results show the average weights, rates of growth, and proportions of the carcase in the different breeds of sheep at 9 months and at 21 months of age (see Tables II and V).

On the average of all breeds the rate of growth declines from 4·7 lbs. per week from birth to 9 months of age to 1·7 lbs. per week from 9 to 21 months of age.

The carcase percentage increases with age on the average from 61 per cent, at 9 months to 65 per cent, at 21 months and with it the percentage of fat from 5·7 per cent, at 9 months to 64 per cent, at 21 months. On the other hand the proportions of pluck, skin and alimentary canal (“Unaccounted for”) decrease with age.

Ratios of early maturity are given for the various breeds and the factors which affect it are discussed.

The average weights, rates of growth and proportions of the carcase are given for the different crosses of sheep (see Tables IX and XIII).

From a comparison of crossbreds with pure breeds it would appear that crossing leads to increase in live weight and probably more early maturity. There is an indication that the proportions of carcase, fat and pluck are less but the proportions of skin and alimentary canal are greater in crossbreds than in the pure breeds of sheep.

There is greater variation in live weight in the Cheviot and Blackface breeds than in the Leicester, Southdown, Hampshire and Suffolk breeds; in the latter breeds variability decreases but in the former breeds it increases with age.

Variability in live weight at 9 months old has steadily increased from 1893 to 1913 but at 21 months old there has been little change.

Some parts are more variable in their proportion to live weight than are others. Fat and alimentary canal are most variable, skin and pluck slightly less variable, while the proportion of carcase is less variable even than live weight.

The variability of the proportions of carcase, pluck and alimentary canal increase while the variability of the proportions of fat and skin decrease with age.

Within a breed and among animals of the same age the heaviest sheep generally have the highest carcase and fat percentage and the lowest percentage of pluck, skin and alimentary canal.

A high proportion of carcase is correlated with a high proportion of fat and a low proportion of skin and alimentary canal at 9 months old. At 21 months old the same holds true with the exception that the sheep with the highest carcase percentage have not the most fat.

The proportion of pluck does not appear to be correlated with any other part of the body except inversely with the live weight.

During the period 1893–1913, although individual breeds show differences, the majority have increased in live weight at 9 months old but at 21 months old have remained practically constant in weight.

The sheep exhibited in 1840 were very much fatter than those shown in the Carcase Classes of to-day and are probably comparable with those of the present-day Live Classes. Since 1840 Leicesters have shown a great increase and Southdowns a small increase in weight.

The carcase percentage of sheep both at 9 and 21 months of age has steadily decreased during the period 1893–1913; this has been attended by an increase in the proportion of pluck, skin and alimentary canal.

There is an indication that the influences which affect sheep in their first year of life (store period) affect their ultimate size.

The seasonal variation in the weight attained by sheep is dependent on the rainfall; a high rainfall through increased root and fodder crops causing increased live weight.

In recent years the measurement of the heat output of animals has taken a prominent place in investigations on the physiology of nutrition, and especially so as regards farm animals. As it is now accepted that the conservation of energy applies to the chemical changes in the living body, the total metabolism can be measured equally well by the indirect or by the direct method. The indirect method using the Douglas bag has been shown by Benedict and others to be simple and satisfactory in the case of human beings, but it is not so easily applied to farm animals, and for these the direct method by the use of a calorimeter has advantages.

Further experiments have been done on the evaporation of water from soil, using the same apparatus and technique as described in an earlier paper. The present series of experiments was designed to investigate the effect of clay content and manurial treatment on the evaporation. Two soils have been used, one containing only 6% clay and the other 15%, and from each soil samples were taken from plots which had received (a) no manure, (b) artificial manure, (c) farmyard manure. The rate at which the soils lost water over concentrated sulphuric acid and at a constant temperature, was found to depend firstly on the amount of clay present, and secondly on the amount of organic material in the soil. The differences due to content of organic material were more obvious in the soil containing the larger amount of clay; the farmyard manure plot lost water at the slowest rate, and the unmanured plot occupied an intermediate position. In the sandy soil the differences in evaporation due to manuring were small.

There is evidence that the moisture equivalent of these soils measures the percentage of water at which the evaporation is first directly affected by the soil particles, and that at percentages of water in excess of the moisture equivalent evaporation is taking place substantially from a free water surface.

A simple experimental method has been described for measuring certain physical constants of soil, using small brass boxes into which soil passing a sieve of 100 meshes to the inch has been packed by hand. The quantities determined are:

(1) The weight of unit volume (100 c.c.s.) of air-dry soil, or the apparent specific gravity.

(2) Amount of water taken up by unit weight of soil.

(3) Pore space.

(4) Specific gravity of the soil.

(5) The volume expansion of unit volume (100 c.c.) of soil when saturated.

The results for one soil only are given, and discussed, to illustrate the method. With the co-operation of the Science Masters Association it is being applied to a number of soils by various schools.

The particular soil used was obtained in six depths as follows: 0–6–12″, 12–18″, 18–24″, 2–3′, 3–4′, and the above constants were determined on each depth. It was shown that (1) and (4) varied inversely with the percentage of clay in the soil, while (2), (3), and (5) varied directly with the clay percentage. The effect on the constants of the larger quantities of organic, matter present in the top two layers of soil was, weight for weight, approximately equal to that of the clay, except in the volume expansion results where the effect if any was within experimental error.

It is possible that the fraction fine silt II, whose upper limit of diameter is ·005 mm., has similar effects to the clay fraction.

Three types of mechanism whereby clay is flocculated by electrolytes, are discussed.

1. Normal or direct flocculation the mechanism of which is precisely that by which electrolytes coagulate electro-negative suspensoids. The isoelectric point theory of such flocculation is assumed in this paper. Experimental evidence is brought forward to show that iron and aluminium salts behave in this “normal” way.

2. Indirect flocculation which takes place whenever the electrolyte reacts with the clay and thereby brings into solution from the clay other substances which cause flocculation. The action of some neutral salts and of acids is regarded as being largely indirect.

3. Abnormal flocculation which is the result of a reaction between the added flocculant and the emulsoid surface of the clay particle. The action of calcium hydroxide is placed under this heading for reasons set forth in the earlier paper.

Because of its obvious bearing on important agricultural operations, the action of calcium hydroxide on clay is considered more fully. The following are the salient points of that consideration:

(i) Although it is reversible to carbonic acid the flocculation of clay by calcium hydroxide is not due to the formation of calcium carbonate. Several experimental results are set forth to show this, the chief is that barium and calcium hydroxides behave quite differently to carbonate and carbonic acid, and alike to clay.

(ii) The action of calcium hydroxide on clay is an action on an “emulsoid gel surface” and not an action on a sol present in gross amount.

(iii) The hydroxyl ion may perform at least two functions in its cooperation with the calcium ion in the flocculation of clay: (a) when added with or after the calcium ion it produces the alkalinity necessary for the reaction between calcium compounds and silica, etc., as discussed in the earlier paper; (b) when added before the calcium ion it not only produces this alkalinity but also peptizes the clay with the production of a greater amount of the emulsoid surface and a consequent increase in the rapidity of flocculation and the volume of the coagulum.

(iv) Critical mixtures of clay and silt—in which neither wholly dominates the system—can be obtained by decantation at an appropriate time during the sedimentation of soil suspensions. It is shown experimentally that when the clay of such mixtures is flocculated more rapidly than the silt, the silt then becomes dominant; and that when the silt is flocculated, more rapidly than the clay, the clay then becomes dominant.

(v) The different behaviour of “clay” and of “silt” to calcium hydroxide is not regarded as due to any essential difference in the structure cf these particles but as being determined by the ratio of the emulsoid surface to the core of the particle. In clay the surface dominates the system, in silt the core dominates the system.

(vi) In very low concentrations the hydroxyl ion appears to behave normally and to militate against the flocculation of clay by calcium salts.

(vii) Organic emulsoids may, in ordinary soils, be partly responsible for the anomalous action of calcium hydroxide on clay, but it is shown that calcium hydroxide exhibits that anomalous action on a deep subsoil clay containing no organic matter.