Interlude

In 1922 discovery was made, proved extremely important. Otto Levi, actually, was not the first one who said the mediators - the transmitters of nervous excitement. Prior to this it was possible to hear that the action of adrenaline reminds "the sympathetic nervous effect, that is, increased heart rate and other effects: batmotropony, inotropic and dromotroponogo. The mediator, as is well known, means the mediator.
So Levi were predecessors. But in the end the case was limited to the statement that the action on the heart of adrenaline reminded the effect of stimulation of its sympathetic nerves, and the effect of stimulation wandering nerve heart had some resemblance to the effect that it has acetylcholine, if you enter this substance in the ventricle. The experience of Levi in the latter case was as follows.
For the experiment consisted of two frog's heart, isolated by the method of Straub, that is fixed on a cannula with craters. The end of the cannula reached cavity ventricle, and funnel extension allowed to fill the heart ringer's solution corresponding to (salt composition) of blood. The latter circumstance was of special significance, because the change of concentration of ions (potassium, calcium, and some other) affects the activity of the heart. The nerves of the heart is wandering and sympathetic - has been maintained at a sufficient period to be laid on the annoying electrodes. Both hearts together with their tubes were mounted on a tripod, and levers were connected to each of the two hearts with feathers, recording heartbeat, both separately.
Slowly rotating drum kymograph, and soot are recorded reductions of two hearts - frog's heart may long to work outside of the body, not supplied with blood. But under the sympathetic nerve, one of the hearts are brought annoying electrodes. Levi includes induction coil, and the reduction of one of the two hearts become more frequent, as expected, in accordance with experiments brothers Zion; a few seconds more frequent work - and Levi takes a pipette ringer solution from one notch, from the one on which hangs irritated heart to another; solution gets into the ventricle of the heart, nerves which are not irritated. It takes another few seconds - and the second heart too starts beating fast and hard, almost as the first. Not exactly as the first, but nearly so.
Wait until the effect will be held (the current is switched off. Refresh solutions in both the tubes. Now Levi irritates the same vagus nerve first heart; it properly, stops for a moment, and then begins to decrease, at first slowly and weakly, then a little harder, but there is nothing new for us not visible until pour pipette solution from the first heart in the second, rather, from the first cannula into the second. Surprisingly, but this time the second heart with a little delay repeats steps first. In any case, the amplitude of abbreviations second heart drops significantly, frequency, however, is not changed.
That's the whole experience. The conclusion of Levi from this extremely important, sensational experiment is the following: irritation of cardiac sympathetic nerves is accompanied by release of their terminala (so called nerve endings) of a substance that causes increased and more frequent cuts, accelerates the initiation of the cardiac conduction system and increases the excitability of the heart, the stimulation of the vagus nerve, too, leads to the selection of its endings of some substance that causes all of the effects that are typical for steel nerves to the heart, already familiar to us. (Honestly, not all, but only one. But science has resolved: all.)
Soon one of the substances was called adrenaline, and the other was called acetylcholine. From this moment in physiology coup: wandering nerves were finally announced specific inhibitory heart, nerves, and sympathetic nerves - specific exciting. The opening of Levi and his co Dale was awarded the Nobel prize. Thus, everything was seemingly very simple, but incredibly complicated. Obviously, therefore, has changed and the teaching of our science.
The reader may remember how in the beginning of the century student and employee I. M. Sechenov Professor of the Baltic Fleet Verigo discussed in detail in the guidance on the physiology of the problem of "two faces" nerves of Zion. After it was delivered to the experience of Levi, the question "two faces" was non-existent. Today about it know, probably only cardiologists. Unfortunately.
No, actually, not to blame for this, that was for scientific opinions: some problems are extremely complicated, others were forced out new requiring urgent resolution. But the problem that we are already used for these poloniecki be called "two-faced", from our point of view, went backstage unfairly. It is too important.
So, there was the so-called mediator theory transfer of excitation and inhibition from the nerve to the Executive body. We will not touch on here how this theory explains the transfer of excitation skeletal, striated muscle, we will note only that the opposite action of the neurotransmitter acetylcholine, which influence on the heart and causing a reduction in skeletal muscle, is obvious. But since we are talking about circulation, have to consider some provisions of the mediator of the theory as applied to the heart, because it is here that first appeared contradictions between the theory and the facts, the explanation of which requires a known tension, if we consider the adrenaline and noradrenaline, outdoor later, as agents, invariably leading to the same result - stimulation of cardiac activity, and acetylcholine as fatally current brake.