No abstract

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.

No abstract

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

No abstract

Peripheral effects of substances acting like nicotine have already been demonstrated with certainty at two sites, the receptive area of the ganglion cell and the motor end-plate. Evidence suggesting that nicotine-like substances act at sensory nerve endings is presented in this paper. Sensory endings resemble the other sites at which nicotine is known to act in that they are places at which propagated impulses are initiated. The possibility of such nicotine-like action was suggested by Coon & Rothman's (1940) description of an axon reflex initiated by acetylcholine. They showed that intradermal-injections of acetylcholine caused an erection of hairs which was not confined to the site ofinjection and was not abolished by atropine. It disappeared after degenerative section of the post-ganglionic sympathetic supply to the area examined.Our experiments have shown that the close arterial injection of acetylcholine or nicotine into skin and mesentery causes a discharge of impulses in the sensory nerves, and evidence is given that this may be a direct effect upon the endings exposed to the drugs.A preliminary note on the experiments described here has already been published (Gray, 1947 a). METHODSThe experiments have been carried out on dogs and cats anaesthetized with nembutal or chloralose and also on cats decerebrated under ether. Preparations of skin and mesentery were used. Skin preparation. Either the skin over the external aspect of the lower part of the thigh or that over the internal aspect of the upper part of the thigh was used. The main cutaneous vessels of the region were dissected and a convenient small branch, supplying a circumscribed area, was chosen. The nerve associated with the smaller vessel was freed from connective tissue and divided for subsequent recording from its peripheral end. A fine hypodermic needle without bevel was then inserted, in a central direction, and tied into the main artery peripheral to the origin of the side branch. The main artery, central to the side branch, was cleaned to receive a bull-dog clamp, and all other branches between the cannula and the eventual site of the bull-dog clamp were double-tied and divided. The nerve alongside the branch artery was then placed on fine brush electrodes, which were moistened with Locke's solution and bound lightly, almost to the tips, with a fine silver wire. In some preparations the whole area of skin supplied by the small artery and nerve was dissected free, except for a pedicle consisting of the artery, vein and nerve (Fig. 1).

No abstract