due to fibrillary contraction, or really auricular fibrillation--in
other words, irregular stimuli proceeding from the auricle--and that
such an irregular pulse is not due to disturbance at the
auriculoventricular node, as believed a short time ago. These little
irregular stimuli proceeding from the auricle reach the
auriculoventricular node and are transmitted to the ventricle as
rapidly as the ventricle is able to react. Such rapid stimuli may
soon cause death; or, if for any reason, medicinal or otherwise, the
ventricle becomes indifferent to these stimuli, it may not take note
of more than a certain portion of the stimuli. It then acts slowly
enough to allow prolongation of life, and even considerable
activity. If such a heart becomes more rapid from such stimuli, 110
or more, for any length of time, the condition becomes very serious.
Digitalis in such a condition is, of course, of supreme value on
account of its ability to slow the heart. Such irregularity perhaps
most frequently occurs with valvular disease, especially mitral
stenosis and in the muscular degenerations of senility, as fibrosis.

Atropin has been used to differentiate functional heart block from
that produced by a lesion. Hart [Footnote: Hart: Am. Jour. Med. Sc.,
1915, cxlix, 62.] has used atropin in three different types of heart
block. In the first the heart block is induced by digitalis. This
was entirely removed by atropin. In the second type, where there was
normal auricular activity, but where the ventricular contractions
were decreased, atropin affected an increase in the number of
ventricular contractions, but did not completely remove the heart
block. He adopted atropin where the heart block was associated with
auricular fibrillation. The number of ventricular contractions was
increased, but not enough to indicate the complete removal of the
heart block.