Geochemical variations in modern subduction-related igneous suites with respect to arc ‘maturity’ in time and space are illustrated using data for both volcanic suites (basalt, andesite and dacite) and intrusive granitoid suites (diorite, tonalite/granodiorite and granite) from circum-Pacific arcs. Using trace element data we suggest that two groups of processes control the natural variation in the parental magmas of both suites: (a) subduction-zone enrichment of lithospheric mantle, locally coupled with crustal assimilation allied with fractional crystallization (AFC) in zones of thickened crust, all of which yield magmas with enhanced concentrations of the large-ion lithophile (LIL) elements K, Rb, Th, U, LREEs, etc; (b) with increasing distance from the active trench, contributions from within-plate sub-continental lithosphere producing mantle-derived magmas with enhanced levels of high-field strength (HFS) elements, among which Nb, Ta, Hf and Y are particularly distinctive. Thus, even for the evolved granitoids of intrusive arc series, ratios of HFS/LIL elements not significantly affected by crystal fractionation, such as (Ta, Nb)/(K, Rb, La), may throw some light on the origin of mafic-intermediate precursor magmas. In terms of these elements we suggest the following groupings for interpreting the tectonic associations of granitoid suites. 1. Primitive, calcic arc granitoids with low LIL and HFS element abundances. 2. Normal, calc-alkaline continental arc granitoids with enhanced LIL element abundances and low HFS/LIL ratios. 3. Mature alkali-calcic arc granitoids with high levels of LIL and HFS elements and higher HFS/LIL ratios. 4. Back-arc/anorogenic alkaline granitoids with the highest levels of HFS elements.

Polymer emulsions will undergo film formation upon loss of water if the driving force provided by capillary pressure is sufficient to overcome the resistance of the polymer particles to deformation. The conditions for film formation are expressible in terms of the surface tension and particle size of the dispersion, the time available for the drying process, the temperature, and the rheological properties of the polymer.

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Two accounts have recently appeared of the effects of an interpolated tetanus on the response of striated muscle to a series of regularly spaced, single motor-nerve volleys. Rosenblueth & Morison [1937] have recorded increases in twitch response as a result of tetani and a relief of partial curarization by the same means. Guttman and others [1937] have made similar observations on frog's muscle, and have concluded that the phenomenon is due to peripheral accumulation of a chemical mediator, which might be "acetylcholine or adrenine". As R o senblueth and M oris o n point out, the long duration of the effects makes it improbable that acetylcholine should, in the mammal, be responsible for them, and they suggest that a mobilization of potassium ions offers a more reasonable explanation of the phenomenon.In the present paper, the phenomenon of enhancement of twitch tension by a tetanus has been examined in detail, and evidence is advanced that it is due in part, at least, to potassium mobilization in the muscle fibre, and that the neuromuscular transmitting apparatus is not necessarily directly involved. METHODSCats decerebrated under preliminary ether aneesthesia were used in the great majority of the experiments. A few were done under chloralose aneasthesia, but we are under the impression that anaesthetics interfere to some extent with the phenomena under investigation.Gastrocnemius, soleus and tibialis anterior have been chosen for recording. The tension was recorded by either a Sherrington torsion-wire myograph or a flat-spring myograph of similar characteristics. The methods used for close arterial injections have already been described 1 Fellow of the Rockefeller Foundation.

IT may now be taken as established that the vagus exerts its inhibitory action on the heart by liberating a substance which biological tests have been unable to distinguish from acetylcholine and which in this paper will be called A.C. substance (see Feldberg and Krayer [1933] for a recent survey of the evidence). Three problems arise out of this first important step towards a solution of the vagal action on the heart:(1) How do impulses in the postganglionic nerve fibres of the vagus liberate A.c. substance? (2) What factors govern the transport of A.c. substance from the region of its liberation to the site of its action? (3) How does A.c. substance exert its inhibitory effect on the heart, e.g. how does it act on the rhythmic mechanism of the pacemaker? This paper and the next are for the most part concerned with the third problem, but some of the evidence also bears on the first and second problems. In the present paper a detailed study has been made of the effect on heart rate produced by a single volley of impulses down either the right or left vagus of the cat. A preliminary account of some of this work has already been published [Brown, Eccles and Hoff, 1932].The inhibitory effect of single stimuli applied to the vagus was first described by Donders [1868], who found that the slowing of the heart rhythm persisted for several beats. Niiel [1874] stated that a single stimulus to the frog's vagus had no effect on the heart, but Heidenhain [1882] found that a very definite slowing was produced. Gaskell [1883] observed that a single shock applied to the vagus produced a prolonged diminution in the contraction of the tortoise heart, and recently Gilson 14-2