It has been recently indicated that relaxation of the guinea-pig taenia by Q-adrenergic stimulants or papaverine is associated with increased concentration of cyclic AMP (cyclic adenosine-3', 5'-monophosphate) in the cells (1-5). On the other hand cyclic GMP (cyclic guanosine-3', 5'-monophosphate) is present in considerable amounts in various mammalian tissues, particularly in the gastrointesti...

SENSATION AND PERCEPTION provided the starting points for modern research into our mental processes. In the early nineteenth century the French philosopher Auguste Comte argued that the study of behavior should become a branch of the biological sciences and that the laws governing the mind should be derived from objective observation. Comte's new philosophy, which he called positivism, was infl...