In a recent paper Burn and Kottegoda (1953) have described the action of eserine on the isolated auricles of the rabbit heart. They found that in most preparations low concentrations decreased the rate of beating, though in some they increased the rate. Higher concentrations always decreased the rate and finally arrested the contractions, and then the auricles were found to be electrically inexcitable. The effect on the amplitude of contraction was different, for low and medium concentrations increased it; high concentrations, however, reduced it. It was stated that the effect of eserine was likely to be that of an anticholinesterase, since DFP had a similar action on the rate leading to arrest of the beat, while neostigmine in high concentration had a different action, increasing the rate, neostigmine being known (e.g., from the work of Riker and Wescoe, 1946) to have an action of its own in addition to its action as an anticholinesterase.In the following account we describe some experiments which appear to relate the action of high concentrations of eserine to the action of quinidine, and we describe also the effect of various other anticholinesterases on the auricles. We have also examined the effect of (1946) that it is a substance which has been shown to reduce the action of acetylcholine (ACh) in all forms of muscle. Thus in the presence of quinidine not only the stimulant action of ACh on the frog rectus and the rabbit intestine is reduced, but also the inhibitory action on the rabbit auricles.A small concentration of ACh (0.16 x 1O-" g./ml.) caused a slight inhibition of rabbit auricles as shown in Fig. 1. When this concentration was applied in the presence of eserine 10-6 g./ml., the contractions were arrested. This effect of eserine was described by Webb (1950). The contractions were resumed when the bath fluid was changed. The arrest was produced a second time by the same concentrations of eserine and ACh, and quinidine (1.5 x 10-g./ml.) was then added. The contractions began again. This result was contractions of isolated auricles in 35 ml. bath. At A 0 6 fsg. ACh. At W the d was changed. At E, eserine 10-6 g./ml. At Q, 0-5 mg. quinidine was added. The numbers above the record are the rate per min.

In the experiments carried out to demonstrate humoral transmission at the neuromuscular junction, Dale, Feldberg & Vogt (1936) showed that the stimulation of the motor nerve while the muscle was perfused with eserinized Ringer's solution was -followed by the appearance of acetylcholine (ACh) EXPERIMENTAL METHODSFreshly excised rabbit hearts were perfused at 35-37°C with Locke's solution (containing 0 05 % NaHCO3 and 0-1 % dextrose) until all traces of blood were removed and the beat was well established. The reservoir in the water-bath above the heart, having been emptied of Locke's solution, was then refilled with about 30 ml. Locke's solution containing eserine sulphate 4 x 10-6g/ ml. From the reservoir the solution ran down a jacketed tube to a cannula tied in the aorta. The heart was enclosed by a glass cup, in the bottom of which the perfusate collected and ran out through a tube which then turned horizontal for a distance of about 17 cm. At the end of the horizontal tube the perfusate was carried vertically upwards by a stream of oxygen, and so back to the reservoir. The perfusing fluid was thus circulated through the heart and back to the reservoir for 40 min or longer during which samples were withdrawn to test on the dorsal muscle of the leech. In some experiments when the fluid was withdrawn it was replaced by fresh solution for a second period of perfusion.To obtain the active material in the perfusate in a more concentrated form, it was taken to dryness by the process of 'freeze-drying'. The residue was extracted with absolute ethanol saturated with NaCl, using 7-5 ml. ethanol for the residue from 30 ml. perfusate. The alcoholic extract was then taken to dryness at a temperature not exceeding 400 C under reduced pressure.The residue was dissolved in 2-5 ml. of a mixture of 1-65 ml. frog saline (0-7 % NaCl solution) and 0-85 ml. distilled water.The extracts so prepared were tested on cat blood pressure, frog heart and frog rectus muscle.For the blood pressure cats were anaesthetized with chloralose; when small amounts of ACh did

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