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Analytical expressions for the non steady separation factor of an isotopic multicomponent mixture in a thermal diffusion column are given. The results, which are appropiate for column operation at total reflux and cover the real case in which small non active end volumes are present, show a simple exponential rising of the logarithm of the reduced separation factor independent of the initial mixture composition. This fact is confirmed by experimental transient data previously reported by Brun et al. and by new experimental work presented here. It is shown that the relative variations of the relaxation time with the hot wire temperature and with the operation pressure are just those predicted by the Furry, Jones and Onsager theory. It is concluded that two experimental operations: steady-separation vs pressure and non-steady separation vs time, and the use of FJO theory will allow us the qualitative prediction of the column operation in the usual temperature and pressure range in laboratory operation

The genetic study of two dwarf and spontaneous mutants of the diploid free-living nematode C. elegans, has been realised according to the particular methods imposed by the unbalanced self-fertilizing hermaphroditism usual to this animal and by the absence of fertility of the male mutants. By combining crosses of hermaphrodite homozygous dwarfs with exceptional heterozygous males and the study of the progeny obtained by automixis of the hermaphrodite hybrids, it can be shown: The embryologic determination of dwarfness could correspond to a perturbation of the eutelie caracteristic of the nematodes.

Analytical solutions for the time evolution of the separation factor Q of an isotopic binary mixture in a thermal diffusion column with small reservoirs (dead spaces) at its ends are given. The simple expression obtained is checked against the numerical solution of the evolution differential equation. This shows its reliability to predict the nonstationary separation factor of a column with dead spaces up to 40% of its active volume, and for equilibrium values of lnQ up to 2 with no restrictions in the isotopic composition of the mixtures. These conditions take account of most of the experimental range that corresponds to the one stage units operating under total reflux. The obtained results support an empirical relation for the relaxation time proposed in a previous work.

From the study of non-steady-state separation in a hot-wire thermal diffusion column, it is shown that the experimental results for the magnitude H02/ mu (Kc+Kd) are proportional to the theoretical values predicted by the Furry-Jones-Onsager (FJO) formulation. This result, together with the earlier ones concerning the similar relations fulfilled by the logarithm of the maximum separation factor and the optimum pressure, ensures that the FJO theory is able to predict the experimental values of the three column constants H0, Kc, and Kd, with the exception of a multiplicative temperature-independent constant, for Kr gas in the temperature range 300-1100 K.

Summary. Rat blastocysts, flushed from the uterus at the moment of the initiation of the implantation process and observed in vitro by time\x=req-\ lapse cinematography, were seen to undergo a series of contractions and dilatations. By these movements, vesicles, containing granular material, emerged through the zona pellucida into the culture medium. In all species so far studied, the earliest known step in the series of interactions between the ovum and the endometrium which lead to implantation, is an increase in the permeability of the endometrial capillaries surrounding the blastocysts. In the rat, this early response of the sensitive endometrium to the presence of the blastocyst is manifested on the afternoon of the 5th day of pregnancy. As the volume of the blastocoele is considerably reduced in most of the blastocysts recovered from the uterus at this moment, it has been suggested that components of the fluid released from the blastocoele may constitute the stimulus for inducing the vascular changes in the endometrium (Psychoyos, 1967). In this paper, we report observations by time-lapse cinematography on the behaviour of blastocysts obtained from Wistar rats at noon on the 5th day of pregnancy (106 hr after the estimated time of ovulation) by flushing the uterine lumen with Tyrode. The culture medium was Eagle L medium containing 5% of foetal calf serum (DIFCO). After being rinsed three times in this medium, blastocysts were picked up in groups of four to five in a small drop of medium and were placed under paraffin oil in a plastic tissue culture dish; the culture dish was then placed under a microscope kept in an ambient temperature of 37° C and in a humid atmosphere containing 5 % C02 in air (Bitton-Casimiri & Psychoyos, 1968). A film at the rate of one frame per minute was taken, using a 16 mm Paillard Bolex camera, adapted to a time-lapse photographic apparatus (Wild). When recovered from the uterus, the blastocysts were still surrounded by an apparently intact zona pellucida. From the beginning of their life in vitro, they were seen to undergo a series of dilatations and contractions. These movements lasted for a period of about 48 hr, during which the zona pellucida ruptured and the blastocysts abandoning it started to dilate. During phases of dilatation, the volume of the blastocoele increased progressively over 5 to 6 hr, until the whole blastocyst reached a maximum size of about 150 µ diameter. A sudden, strong contraction, completed in less than 60 sec, then occurred, reducing the