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The features of the health technology cycle are presented, and the effects of the demographic, epidemiologic and economic transition on the health technology demand in Mexico are discussed. The main problems of science and technology in the context of a decreasing scientific and technological activity due to the economic crisis and the adjustment policies are also analyzed: administrative and planning problems, low impact of scientific production, limitations of the Mexican private sector, and the obstacles for technology assessment. Finally, this paper also discusses the main support strategies for science and technology implemented by the Mexican government during the 1980s and the challenges and opportunities that lie ahead.

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Population increase, rural-to-urban migration, excessive population concentration side by side with scattered rural populations, and the economic crisis provide the primary framework for this analysis of health manpower in Mexico. The secondary frame of reference is the primary causes of mortality (in 1981): the leading cause, accidents and violence; the second, heart disease; the third, influenza and pneumonia; and the fourth, enteric diseases and diarrheas. Data are supplied on the number of new physicians graduating (this number rose from 2,493 in 1976 to 14,099 in 1983), and on the number of nurses (about 98,000, of which 40% are professionals). The growth pattern of the contingent of dentists is the same as that of physicians, namely, disproportionate and inefficient. The Federal Government is now trying to set up a National Health System that will fulfill the constitutional right of all Mexican citizens to health protection. On the basis of the disequilibrium apparent in every part of the health sector, the author recommends that educational and health institutions plan and coordinate the training of physicians so that the number of graduates may meet the country's needs, and the quality of their education may be improved.

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We have developed a convenient system for genetic analysis of Salmonella typhi exploiting the properties of the mutator phage Mu. In spite of the fact that wild-type Salmonella typhi strains do not allow Mu to form plaques on them, we have shown that these strains are actually sensitive to the phage. It proved possible to use Mu to induce mutations and to promote intra- and interspecific genetic transfer, without having to introduce the phage into the bacteria by means other than infection. Furthermore, we isolated Salmonella typhi derivatives on which Mu formed plaques, and studied the behaviour of Mu in these and wild-type strains.

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Population increase, rural-to-urban migration, excessive population concentration side by side with scattered rural populations, and the economic crisis provide the primary framework for this analysis of health manpower in Mexico. The secondary frame of reference is the primary causes of mortality (in 1981): the leading cause, accidents and violence; the second, heart disease; the third, influenza and pneumonia; and the fourth, enteric diseases and diarrheas. Data are supplied on the number of new physicians graduating (this number rose from 2,493 in 1976 to 14,099 in 1983), and on the number of nurses (about 98,000, of which 40 per cent are professionals). The growth pattern of the contingent of dentists is the same as that of physicians, namely, disproportionate and inefficient. The Federal Government is now trying to set up a National Health System that will fulfill the constitutional right of all Mexican citizens to health protection. On the basis of the disequilibrium apparent in every part of the health sector, the author recommends that educational and health institutions plan and coordinate the training of physicians so that the number of graduates may meet the country's needs, and the quality of their education may be improved (Au)

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An unusual Escherichia coli K12 mutant for carbamyl phosphate synthetase is described. The mutation was generated by bacteriophage MUI insertion and left a 5% residual activity of the enzyme using either ammonia or glutamine as donors. The mutation is recessive to the wild-type allele and maps at or near the pyrA gene, but the mutant requires only arginine and not uracil for growth. By a second block in the pyrB gene it was possible to shift the accumulated carbamyl phosphate to arginine biosynthesis. The Km values and the levels of ornithine activation and inhibition by UMP were normal in the mutant enzyme.

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The genetic transformation of Escherichia coli K-12 with chromosomal deoxyribonucleic acid purified from Salmonella typhi is described.

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Temperate bacteriophage Mu-1 was used to generate a lysogenic derivative of the F'lac episome of Escherichia coli. Intact, covalently circular molecules of F'lac and lysogenic F'lac Mu(+) deoxyribonucleic acid (DNA) were isolated and examined by electron microscopy. The mean contour lengths of F'lac and F'lac Mu(+) molecules were 37.6 +/- 0.4 mum and 53.2 +/- 0.4 mum, respectively. The mean difference, 15.6 mum, is similar to the mean contour length of 12.9 +/- 0.1 mum obtained for linear DNA molecules released by osmotic shock from mature phage Mu-1 virions. These results provide direct physical evidence that phage Mu-1 integrates by linear insertion of its genome into the DNA of lysogenic host bacteria. Chemical and physical analyses of phage Mu-1 DNA indicate that it is similar to E. coli DNA in respect of gross base composition, buoyant density, and melting temperature.

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