were made. All species of spermatozoa tested, including those highly sensitive-to an increase in osmotic pressure, were fully motile in 20M glycerol. It is most unlikely that cells impermeable to glycerol would retain motility in the presence of such an excessive external osmotic pressure, and the retention of motility in the presence of high concentrations of glycerol was taken as evidence that the cells were permeated by this solute. Other neutral solutes can to some extent protect spermatozoa against damage by freezing and thawing (Smith & Polge, 1950), but none is as effective as glycerol. SUMMARY 1. The spermatozoa of the rabbit, the bull, the fowl and the herring were subjected to freezing and thawing in media containing various concentrations of glycerol, and observations made of the resulting changes in motility of the spermatozoa. 2. These observations indicated that the damage suffered by the spermatozoa during freezing and thawing was caused-by their exposure to excessive concentrations of salt when water was removed as ice. 3. The concentration of electrolyte above which irreversible damage occurred was characteristic for the spermatozoa of each species tested. The protective action of glycerol was due to its ability to prevent the salt concentration rising above this level.

Ever since the demonstration of the uniform life span of the red cell from the linear curve of disappearance of transfused normal cells in healthy recipients, it has been clear that their disappearance from the circulation is a result of an ageing process. Many people have looked for differences in behaviour and constitution which might reflect the heterogenous nature of the cells of a normal blood sample.Differences in density between reticulocytes and mature red cells have been known for some time, and it has been claimed that by centrifugation young and old cells can be separated (Borun, Figueroa & Perry, 1957). In the present investigation blood samples were centrifuged in 30 % bovine albumen, a medium in which it was found that small differences in red cell density were readily demonstrable, and the cells at different depths of the centrifuged column were analysed by a variety of chemical procedures. METHODSTwenty millilitres of blood was taken from donors into 10% ethylenediamine tetra-acetic acid (EDTA) and centrifuged at 2000 g for 10 min. The supernatant plasma and white cell layer were removed and the packed cells mixed with an equal volume of 30% bovine albumen in a narrow tube (diam. 1-0 cm.). When fully suspended the mixture was centrifuged at 4000 g for 10 win and then at 10,000 g for 5 min at 40 C. After this the supernatant plasma was completely removed with a fine pipette and appropriate samples of cells withdrawn from the top and bottom of the column of packed cells. These samples were finally recentrifuged under the same conditions and a top fraction from the original top sample, and a bottom fraction from the original bottom sample, used for analyses.59Fe W&belling of cell. Healthy donors were given 75 ,uc of 59FeCl3 intravenously and blood taken from them 5 days after injection. At this time 90 % of the radio-iron is found in circulating red cells (Joske, McAlister & Prankerd, 1956). The blood was then treated as above. After centrifuging at 10,000 g, 0-5 ml. of packed cells was removed from both top and bottom of the cell column. These were haemolysed in 3.5 ml. of water and their radioactivity assayed in a well-type scintillation counter; at least 1000 counts were recorded on each sample. To correct for any discrepancy between the packing of cells at the top and bottom of the centrifuged column the haemoglobin concentration of the final solution of haemolysed cells was estimated by the cyan-21-2

No abstract

The experiments described here were carried out to see whether the rate of extrusion of Na from human erythrocytes is affected by their rate of production in the body and by their shape. The latter variable has to be introduced because cells obtained from those pathological conditions (haemolytic anaemias) in which cell turn-over is rapid are often spherocytic, and this change in shape might contribute to altered behaviour. A control for this point has been obtained by examining normal cells in iso-and hypotonic media. Cells from cases of pernicious anaemia were taken as typical of a low rate of turn-over in the body, but it is possible that these cells were abnormal for reasons connected with their distorted shape rather than with their low rate of production. As far as conditions permitted experiments have been made on subjects before and after therapy in order to see whether a change towards a more normal rate of cell production caused the activity of the cells, as measured by the rate of Na excretion, to approach that of cells drawn from healthy individuals.As the validity of any comparison which may be made between the results of successive experiments depends upon the reproducibility of behaviour of normal cells this has also been studied. METHODSTracer 8Odium effiux Cells were prepared containing a trace of the radio-active isotope "Na. 2-5 ml. (depending upon the age of the "Na preparation) of isotonic NaCl, prepared from irradiated NaHCO3, was added to 5-10 ml. of whole, heparinized blood. The mixture was incubated at 37.50 for 2 hr except when otherwise stated. A shorter time of incubation could be used without affecting the results, but longer times, as described later, introduced uncertainty on account of deterioration of the cells. The cells were spun down in a graduated tube at 1500 rev/min (14 cm radius) for 10 min. In order to reduce the quantity of radio-active extracellular solution the cells were re-suspended in about 10 ml. of warm isotonic solution (the composition is specified later) and centrifuged again. SODIUM EXTRUSION FROM ERYTHROCYTES 471About 1-5 ml. of cells were added to 100 ml. of the saline medium. The suspensions of cells plus medium were contained in inverted polythene bottles, the normal openings of which were closed by means of rubber bungs; two holes were drilled in the bases so as to permit sampling and the introduction of a tube carrying gas for oxygenation and stirring. The gas used was 95 % 02 and

Summary In a double‐blind trial of folic acid supplements (5 mg. per day) during pregnancy‐no effects were seen in the incidence of anaemia or complications of pregnancy, although the serum folate levels were less abnormal in the treated group. Nor was evidence found that anaemia or serum folate levels determined the incidence of complications and the outcome of pregnancy. No justification for giving routine folate supplements to this population of patients was apparent.