EFFECT OF NICOTINE 133 



ACTION" OF NICOTINE 



Experiment 3. — Arrange a heart to record as before, having previously 

 isolated one vagus and placed it upon a pair of electrodes. Test the vagus 

 to see that it causes inhibition on stimulation. Eecord a few normal beats 

 and then apply a few drops of aO'l per cent, solution of nicotine in normal 

 saline. The heart is slowed for a few beats and then beats rather quicker 

 than before. Now stimulate the vagus. There is no inhibition. Apply the 

 electrodes to the crescent. The heart is inhibited. 



The action of the drug in a weak solution is to first stimulate nerve 

 cells and then to paralyse them. The stimulation is shown in the 

 inhibition, which may be but slight or fairly well marked, according to 

 the strength of the solution. After a few beats the heart regains its 

 rate, and may even become quicker and the force greater than before 

 (i, fig. 104). In ii is shown the effect of stimulation of the vagus. No 

 inhibition or slowing follows even with strong stimuli, though previously 

 the inhibitory effect had been very readily produced. During the 

 stimulation an augmentor effect is produced, the height of the beat 

 becoming 235 mm. as compared with 21 mm. There is only slight 

 acceleration, and both effects gradually die away. In in is seen the 

 effect of stimulation of the sinus. It is perfectly characteristic of 

 the result given by a normal heart (fig. 101, in). All these three 

 tracings were taken quickly one after the other, and then moi^e nicotine 

 solution was applied. It was then found that stimulation at the sinus 

 no longer produced inhibition. "With weak currents no effect at all 

 was perceived except a slight acceleration. The strength of the 

 stimulus was then considerably increased, when marked acceleration 

 was produced lasting as long as stimulation continued. On cessation of 

 stimulation the heart was inhibited, but after a time recommenced 

 beating with a rhythm at first slow, but gradually increasing until the 

 original' rate was once more attained. 



This experiment is of great importance because it affords an ex- 

 cellent example of the value of nicotine, as it is now employed for 

 determining the position of nerve cells on the course of visceral nerve 

 fibres. It is found to first stimulate these cells and then paralyse 

 them, and if the dose be increased the nerve fibres themselves also 

 become paralysed. This is a general rule for all visceral nerve 

 fibres and cells, and in the experiment as above carried out proves 

 that cells are interposed on the course of the vagus fibres, and are 

 situated in the region of the crescent ; but that on the other hand the 

 sympathetic fibres run straight to their terminals without havi un- 

 nerve cells interposed on their course within the heart. 



