 565  517. Although harmonic generation has long been used by the microwave spectroscopist, the process has been generally rather laborius. Involving critical, hand-made units, it often took hours, or even days, to adjust. The requirement therefore, existed for a replaceable cartridge unit which could be readily inserted into a mount and set for optimum operation with a minimum of controls. 518. The method used was that originated by Mitra using a pulse transmitter and three receiving aerials, the latter being spaced a wave-length apart two directions. The records obtained were analyzed by the method of identifying similarities in the fading patterns and providing that the fading was of a suitable irregular time, mean time displacements of the signals were interpreted as revealing a constant drift of irregular patches of ionization in the F-region. 519. In uninfected HeLa cells the label appeared predominantly over nucleoli with small amounts scattered throughout the nucleoplasm. Cells infected for 2 hours incorporated tritiated cytidine in a similar manner. At subsequent intervals, however, the label was more diffusely distributed over the nucleoplasm, and by the 8th hour, there was little if any nucleolar labeling of RNA in infected cells. 520. As early as 1774 the Academy of Bavaria had offered a prize for the best dissertation in answer to the question «Is there a real and physical analogy between electric and magnetic forces?» Prof. J. H. van Swinden of Holland replied, in conclusion, that the similarities were entirely superficial and that the two forces were essentially of different kinds. A contrary position was taken by Professors Steighkehner and Hubner in 1773 and 1780 that such related forces must have their origin in a single agent. The full resolution of the question continues into our own time. 521. Almost all organisms require oxygen for the maintenance of life. We human beings obtain this oxygen from the air we breathe. This is passed into the lungs where the oxygen is absorbed through the walls of the alveoli in exchange for carbon dioxide. Air consists in the main of oxygen (just over one fifth by volume) and nitrogen with a small percentage of water vapour, carbon dioxide and the rare gases. Oxygen is absorbed into the bloodstream via the lungs, the air exhaled picking up water vapour and carbon dioxide from the body. 522. We have surveyed a field in the throes of almostfrenetic experimental activity. Development has been so rapid that there has been little time for stock-taking. There are so many things to do, so many facts to gather, so many experiments to be conformed or which require additional controls that, for the moment, it seems wiser to be wary of far-reaching conclusions. Much more has been discovered of what has to be learned than has emerged as firmly established knowledge. 565 |
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