C. E. Ford

A suspension is made in isotonic (2.2%) sodium citrate solution from the contents of the tubules from a whole testis or a testicular biopsy specimen. The germinal cells are sedimented by centrifuging, leaving most of the sperm in the supernatant fluid, which is discarded. The cells are resuspended in hypo-tonic (1%) sodium citrate solution and left to stand at room temperature for 12 minutes, after which they are sedimented again and fixed as a concentrated suspension in a mixture of 3 parts absolute ethyl alcohol to 1 part glacial acetic acid plus a trace of chloroform. Two quick changes into fresh fixative follow. Air-dried preparations are made from the final fixed suspension and stained in lactic-acetic-orcein. The method is suitable for stages of male meiosis in which the chromosomes are condensed. Its principle advantage is the separation of the clumps of spermatogonia and spermatocytes into individual cells which are randomly dispersed over the preparations. Compared with squash techniques, the air-drying method gives improved spreading of the chromosomes and less cell breakage.

The method was developed for bone marrow of mice but is applicable to other tissues and other species of small mammals. Mice are injected intraperitoneally with 0.5 ml of 0.025% colchicine solution and killed 1 hr afterwards. The femurs are dissected out rapidly, the epiphyses are removed, and the marrow is washed out of the shafts by warm hypotonic sodium citrate solution from a hypodermic syringe. Gentle aspiration of the marrow into and out of the syringe converts it into a fine suspension. The suspension is kept in the citrate solution at 37°C for 10 min. Connective tissue and bony spicules are removed by centrifuging through Nylon bolting cloth in a bacterial filtration tube, before fixing in acetic-alcohol (1:3) and staining by the standard Feulgen procedure. The cells are concentrated for each change of reagent by centrifuging slowly. The advantages of colchicine pretreatment and of working with cell suspensions are emphasized.

From the results of 747 experiments on dry basic and ultrabasic magmas and related synthetic systems equations have been derived which predict the olivine/liquid cation partition coefficients for Mg (correlation coefficient r = 0·996), Fe2+ (r = 0·993), Ca (r = 0·79) and Mn (r = 0·70) as a function of temperature, pressure and liquid composition. The ratio of the partition coefficients for Mg and Fe2+ (KD) varies from 0·25 to 0·38. For any given magma composition liquidus olivines are slightly more iron-rich at high pressures than they would be at low pressures. The Mg and Fe2+ partition coefficient equations may be used as geothermometers which are accurate to better than ±1 per cent if pressures can be estimated by independent methods. Minor element partition thermometers (Ca and Mn) are too sensitive to analytical errors, or to departures from equilibrium, to prove reliable. Temperatures may also be obtained from a geothermometer based on the concept of olivine saturation. This is independent of olivine composition and can be used where these is evidence of disequilibrium between olivine and host liquid. In such a situation the errors indicated by the Mg and Fe2+ partition thermometers are asymmetric about the true temperature except when the equilibrium olivine composition is Fo50. These geothermometers are sufficiently sensitive to demonstrate magma mixing. The partition coefficient equations may be used to model equilibrium crystallization of olivine even though the partition coefficients, and the ratio of the partition coefficients (KD). are continuously changing. Fractional crystallization of olivine may be approximated by sequential removal of small amounts of olivine formed by equilibrium crystallization.