This failure to transmit properly brain messages or this lack of co-ordination may take one of two forms:  it may result in an under-innervation of the organs of speech, which results in loose, uncontrolled repetitions of a word, sound or syllable, or it may take the form of an overinnervation of the vocal organ with the result that it is so intensely contracted as to be entirely closed, causing the “sticking” or inability to pronounce even a sound, so common to the stammerer.

Suppose that you try to say the word “tray.”  Do not articulate the sounds.  Merely make the initial effort to say it.  What happens?  Simply this:  The tip of the tongue comes in contact with the upper front teeth at their base and as you progress in your attempt to say “t,” the tongue flattens itself against the roof of the mouth, moving from the tip of the tongue toward its base.  If you are a stammerer, you will probably find in endeavoring to say this word, that your vocal organs fail to respond quickly and correctly to the set of brain messages which should result in the proper enunciation of the word “tray.”  Your tongue clings to the roof of your mouth, your mouth remains open, you suffer a rush of blood to the face, due to your powerful and unsuccessful effort to articulate, and the word refuses to be spoken.

Now, in order to dissociate “lack of co-ordination,” from stammering and to get an idea of its real nature, let us imagine an experiment which can be conducted by any one, whether they stammer or not.

You see on the table before you a pencil.  You want to write and consequently you want to pick up the pencil.  Therefore, your brain sends a message to your thumb and forefinger, saying, “Pick up the pencil.”  Your brain does not, of course, express that command in words, but sends a brain impulse based upon the kinaesthetic or motor image of the muscular action necessary to accomplish that act.  But for our purpose in this experiment, we can assume that the brain sends the message in terms which, if interpreted in words, would be “pick up the pencil.”  Suppose that when that brain message reaches your thumb and forefinger, instead of reaching for the pencil, they immediately close and clap or stick, refusing to act.  Your hand is unable to pick up the pencil.  That, then, is similar to stammering.  The hand is doing practically what the vocal organs do when the stammerer attempts to speak and fails.  But, on the other hand, if, when the message was received by your thumb and finger, it made short, successive attempts to pick up the pencil, but failed to accomplish it, then you could compare that failure to the uncontrolled repetitions of stuttering.  This inability to control the action of the thumb and forefinger would be the result of a lack of co-ordination between the brain and the muscles of the hand, while stuttering or stammering is the result of a lack of co-ordination between the brain and the muscles of speech.