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This audio-visuo-oral course in English as a second or foreign language is aimed to provide a full year's work for classes of beginners in elementary or high schools. It may also be used for learners outside these age-groups or for remedial or review work. The material is systematically graded and limited to approximately lexical items. The course consists of four volumes: a picture book designed to provide extensive group-work; a drill book for the teacher; a reading book presenting the written forms of the structural and lexical content of the course after it has been introduced orally; and a workbook providing the material for writing practice, to further consolidate the patterns established through the drill book. The course is accompanied by tapes. (AMM)

A study of the mechanical properties of four pear varieties demonstrated that indices of texture obtained by Acoustic Spectrometry, Compression and Shear analyses showed similar patterns of change on ripening. Furthermore, studies on gel model systems indicated that stiffness coefficients obtained from acoustic spectra were influenced by pectin concentration, soluble and insoluble solids. The pectin fraction isolated from two of these varieties showed a trend in dissolution comparable to texture measurements. The data indicate that acoustic spectrometry, like shear and compression analyses, can be a useful monitor of pear texture.

Estimations were made of the numbers of germ cells in the guinea-pig ovary from embryonic stages to maturity. A volumetric method was used to estimate the numbers of oögonia and Oöcytes in animals aged 26 to 55 days p.c., while counts were made of the numbers of germ cells present between 60 days p.c. and 12 months p.p. Neither the mitotic activity of oögonia nor the successive stages of meiotic prophase are closely synchronized. The process of oögenesis ceases at about 50 days p.c. Large numbers of Oöcytes are found in the leptotene stage at 35 days, in zygotene at about 40 days, and in pachytene at 50 days p.c. Thereafter the proportion of Oöcytes in the diplotene phase increases, so that by a few days after birth all the Oöcytes are in this stage. By 1 month p.p., however, two types of Oöcyte in diplotene are found in large numbers. The first is comparable to the corresponding stage in rat, man and the chick, while the second displays a very contracted nucleus. The latter type rapidly gains predominance, and by 12 months p.p. 94 per cent, of the germ cells belong to it. The number of germ cells per ovary increases from about 27,000 at 30 days p.c. to reach a peak of almost 105,000 by 41 days p.c.; subsequently it declines to some 13,000 by 12 months p.p. This decline is caused by a steady process of atresia which affects germ cells from the earliest stages of development.

It is widely accepted that oogenesis normally stops early in mammalian development (see Brambell, 1956; Franchi, Mandl & Zuckerman, 1962). Nevertheless, it has been claimed that mitotically active oogonia, and oocytes in early stages of meiotic prophase occur in mature specimens of Galago senegalensis (Gerard, 1920, 1932; Gerard & Herlant, 1953; Herlant, 1961; Petter-Rousseaux, 1962; Butler, 1964), G. crassicaudatus (Gerard & Herlant, 1953), G. demidoffi (Gerard, 1932; Gerard & Herlant, 1953; Petter-Rousseaux, 1962), Perodicticus potto (Gerard & Herlant, 1953), Loris tardigradus lydekkerianus (Rao, 1927; Brambell, 1930), and Daubentonia madagascariensis (Petter-Rousseaux & Bourliere, 1965). The latter is a lemuroid prosimian, while all the others are lorisoids (Hill, 1953). It has also been asserted that new germ cells are formed by direct transformation from the somatic cells of the ovarian germinal epithelium (Gerard, 1920, 1932; Rao, 1927; Gerard & Herlant, 1953).

A processing system for photocathodes has been developed whereby the variation of the spectral response of the photocathode can be continuously monitored throughout processing. The design details of the system are given together with some examples which show the variation of the spectral response of an S‐20 photocathode during various steps in processing. This system should lead to procedures for controlling the luminous sensitivity in any portion of the visible spectrum, better predictable photocathode‐to‐photocathode uniformity, and reduced processing time.

It is postulated that replication of double stranded DNA involves the sequential addition of microbubbles, containing RNA-primed short nascent DNA pieces, to a macrobubble, followed by covalent attachment of the fragments into longer nascent strands.

The extraction equilibria of the lanthanide chloride systems MC13-HC1-H2O-1 M D2EHPA (in mineral spirits), where M designates Sm, Nd, and trivalent Ce cations, was studied over an extensive range of concentrations. The metal aqueous concentration was varied from 0.05 to 2.0 M and the aqueous acidity ranged from 0.3 to 1.0 M. The equilibrium curves, with the aqueous acidity as a parameter, exhibit a behavior typical of other lower lanthanides. Further, trivalent cerium behaves the same as other trivalent rare earths. A study of the binary extraction systems Sm-Nd, Sm-Ce, and Nd-Ce indicate that the separation factor remained nearly constant for all conditions studied. The arithmetic averages were βsm.Nd ∼ 8.4, βNd.Ce ∼ 2.0, and βsm.Ce∼ 18.9. In the ternary system Sm-Nd-Ce, the separation factor of each combination pair of elements remained essentially constant for all conditions studied. Furthermore, the separation factor of each pair of elements in the ternary system remained the same as in the case where each pair of elements is extracted together.

Marsaglia and Maclaren combined two linear congruential generators in order to produce a pseudo random number sequence uniformly distributed in the range [0,2³⁵]. Their method is a considerable improvement compared with the primitive linear congruential method at the cost of greater generation time. In this thesis, a simple modification of the Marsaglia-Maclaren method is presented in which there is an alleviation of the increased generation time, and a slight further increase in randomness. The modified generator is tested extensively in a variety of statistical tests and simulation problems.