A physicochemical mechanism for magnetic field detection by migratory birds and homing pigeons

Migratory birds and homing pigeons can apparently obtain directional information from the Earth's magnetic field. The effect is difficult to detect, and discussion of the possible process of magnetic field detection by birds seems so far to have foundered on the simple fact that the orientational effect of the Earth's magnetic field on a single electron spin associated with a molecule of animal tissue would be of the order 10(-8) eV--almost certainly too small to be detectable biologically. Here I direct attention to a process which would overcome this basic problem, and which also seems to provide an explanation of all the main features of published data. It is a mechanism in principle only, however, and is discussed here in no more detail than is necessary to clarify the basic ideas and to provide a basis for further investigation.     

Determinant selection is a macrophage dependent immune response gene function

Immune response (Ir) genes are linked to the species histocompatibility complex and define as yet uncharacterised phenotypic products which control the immune response to thymus dependent antigens. Antibody formation and antigen induced T lymphocyte proliferation are two examples of immune phenomena which, in vivo and in vitro, operate under Ir gene influence. To clarify their mechanism of action and cellular location, we have examined the contribution of antigen structure (amino acid sequence and conformation to Ir gene control of antigen recognition by T lymphocytes) as well as to the critical role played by the antigen presenting macrophage in expression of that control. We report that immune response gene control of antigen recognition operates at least in part at the level of the macrophage.     

Influence of PGA1 on cartilage growth

Summary Using the Fell technique of organ culture of cartilage in a chemically defined medium, it has been shown that prostaglandin A₁ at a concentration of 25 g/ml caused chondrocyte death in chick embryonic limb rudiments. An equimolar concentration of PGE₂ was not toxic to the cells.Acknowledgments. We are grateful for the support of C. J. K. by the Medical Research Council and of D. L. G. by the Arthritis and Rheumatism Council for Research. Our thanks are due to Dame Honor Fell, F. R. S. for invaluable advice and guidance, to Dr J. Pike (Upjohn Co.) for supplies of prostaglandin A₁, and to Dr Sylvia Fitton-Jackson for the gift of culture medium.     

Seed germination in response to diurnal fluctuations of temperature

Diurnal fluctuations in temperature may initiate or accelerate germination in certain flowering plants, and the effectiveness of the stimulus varies according to the amplitude of fluctuation and the presence or absence of light. Attempts to assess the adaptive significance of the phenomenon, however, have been limited by the scarcity of data for species of contrasted ecology. We report here an investigation of germination responses to fluctuating temperatures, conducted on seeds of herbaceous species collected from native populations near Sheffield. The results suggest that requirements for diurnal fluctuations in temperature are characteristic of the germination of species from particular types of habitat and provide mechanisms which cause seeds to germinate at times and in places favourable for seedling establishment.     

A new one-step synthesis of hexahydrocannabinoid analogs

Summary A one-step synthesis of hexahydrocannabinoid analogs (HHC) is described making use of the condensation of phenolic ketones and aldehydes with citronellal in the presence of pyridine.Grateful thanks are accorded to Drs L. Chopard and S. Selvavinayakam for spectral measurements and Dr I. Fleming for useful discussion.R. Mechoulam and Y. Gaoni, Recent advances in the chemistry of Hashish, in: Progress in the Chemistry of Organic natural products, vol. 25, p. 175. Ed. L. Zechmeister. Springer Verlag, Wien 1967; R. Mechoulam, Marijuana Chemistry and Pharmacology, metabolism and clinical effects. Academic Press, New York 1973; R. Mechoulam, N. K. McCallum and S. Burstein, Chem. Rev.76, 75 (1976).     

Two monoclonal antibodies against different antigens using the same VH germ-line gene

Immunoglobulin diversity seems to arise largely by three mechanisms: (1) the existence of several germ-line genes, which must be rearranged before expression--that is, V and J for the light (L) chains, V, D and J for the heavy (H) chains; (2) somatic events, including mutations and gene conversion; and (3) combinatorial association of heavy and light chains, leading to the proposal that random pairing of p X H and q X L chains might generate p X q antibody molecules expressing discrete specificities. As heavy and light chains derived from the same immunoglobulin molecule would frequently reassociate preferentially, it is likely that only a fraction of potential heavy--light pairs actually provides "valid' antibodies. As a consequence of combinatorial heavy--light chain pairing, antibodies of discrete specificities sharing the same VH region, associated with distinct light chains (or vice versa) should be encountered. We report here that two heavy chains, derived from the same VH germ-line gene, may be present in anti-NP or anti--GAT antibodies, depending on their association with a specific lambda or kappa light chain, respectively.