HEART-MUSCLE 507 



rotating drum. Note the compound cardiogram, the larger waves repre- 

 senting the tonus of the heart and the smaller vibrations the beats. 

 From ten to forty of the latter occur during one tonus-wave. This 

 phenomenon appears to be widespread if not universal in muscle, but 

 its import is not yet clear. Under certain conditions not yet definable 

 these vasomotor tonal changes occur also in the frog's heart. (See 

 Figs. 157 and 160.) 



Expt. 72. Muscarine andAtropine (its antidote) .(Apparatus : Heart- 

 lever, inductorium with platinum electrodes, muscarine-solution, atropine- 

 solution, frog or tortoise.) Set up the inductorium for alternating cur- 

 rents. Expose the heart, and stimulate the pale "crescent" (between the 

 sinus venosus and right auricle) with strong alternating currents. The 

 heart's beat is more or less inhibited. Now, with a pipet add three drops 

 or so of the muscarine-solution to the heart. It gradually comes to a 

 standstill. Stimulate the ventricle with induction-shocks and observe 

 how little irritable the muscle is. Let it alone a few minutes. Now let 

 fall a few drops of the atropine-solution on the heart. It gradually beats 

 again, perhaps more powerfully than is normal. Stimulate the crescent 

 as before. No inhibition now takes place, for the atropine has paralyzed 

 the neural mechanism of the heart. 



Muscarine is the alkaloid which sometimes kills people who eat poi- 

 sonous fungi. As in this experiment, its action is directly on the heart- 

 muscle and not on the cardiac nerve-mechanism. Atropine, then, is the 

 physiological and therapeutic antidote of muscarine, but it acts powerfully 

 on the nerve-cells in the heart. As these are of inhibitory function (see 

 Expts. 61 and 87), no harm follows. It acts also on the muscular tissue 

 and it is here that it exerts its direct antagonism to the muscarine. 



Expt. 73. Nicotine. (Apparatus: Kymograph, etc., heart-lever, 

 pipet, 0.1 per cent, nicotine-solution, frog, and Daphnia). Expose the 

 heart and make record of its beat on the rotating drum. Now add a few 

 drops of the weak nicotine-solution. The heart slows for a short time 

 and then beats more strongly than before. The slowing is due to a 

 stimulation of the intracardiac inhibitory mechanism, while the aug- 

 mentation of the beat comes from a partial paralysis of the same nerve- 

 cells. Nicotine in small quantity stimulates and then paralyzes the neu- 

 rones, especially the cell-bodies. 



Nicotine for some, probably chemical, reason has a predilection for the 

 cell-bodies of the neurones, exerting no effect on the neuraxones. Exces- 

 sive smoking has on the human heart some of this demonstrated effect, 

 making it irregular and rapid. The stimulating result of the four to- 

 bacco alkaloids is seen in their action on the cerebral cortex: they incite 

 to mental work and abolish to a marked degree the feeling of fatigue. 

 Their action, however, on the nerve-cells of the walls of the stomach is 

 often disastrous to perfect digestion. (See page 169.) Demonstration 

 of nicotine's action on the heart of Daphnia (see Expt. 12). 



Expt. 74. Adrenalin. (Apparatus: Cardiograph, 0.01 per cent, solu- 

 tion of adrenalin chloride in Ringer's solution, frog's heart.) Make a 



