Concentrated paste-like suspensions of fine powders in liquids manifest certain properties, which depend strongly on the degree of packing. The rule given in table 1 was put forward, and was shown to hold in a few cases (2, 3). This rule was considered to be rather a rough guide, since factors such as particle shape, etc., were not taken into account. It would obviously be necessary to investigate the physical side of each of these phenomena more thoroughly, because very little is known about them. But, before doing so, it seemed desirable to compare the behavior of a large number of powders of different kinds to see whether the rule really was a first approximation to the truth, and to detect cases which might be specially fit for more exact investigation. This was the aim of the following * Jet is an intermediate compound between wood and coal, formed from petrified wood under high pressure, and it contains vegetable structures. It is homogeneous, and contains carbon, some 8 per cent of water, and 20 per cent of hydrocarbons, which appear on distillation. It shows a subconchoidal fracture, and is amorphous.t After the gypsum had been ground to the correct size in water in the ball-mill, the excess water was removed by filtration and half of the residue was dried at about 90°C. in a steam oven, and half by exposure to the air for several days. The ovendried sample had lost some of its water of crystallization.SEDIMENTATION VOLUME * This was determined by allowing a known weight of powder to sediment uniformly in a known volume of water or aqueous solution, in graduated tubes having an internal radius of 0.58 cm., calibrated in cubic centimeters

SUMMARYElectromanometric recordings of caecal pressures were made in chronically cannulated ponies. Endoscopy allowed direct observation of the caecal base and cupola while recording intracaecal pressures and enabled a functional interpretation of caecal pressure profiles. Using gas-tight seals, the caecal gas cap baseline pressure (tone) was usually below atmosphere, becoming less negative postprandially. Diurnal variations were observed in the amplitude and frequency of caecal pressure profiles and the direction of caecal movements, during which intra-caecal gas cap pressures briefly became positive. A paraprandial (psychic) phase of enhanced caecal motility was observed. Manipulation of the caecal gas cap volume, by insufflation of nitrogen gas, demonstrated the capacity of the caecal base to regulate gas pressures and to eliminate fermenting gases.