Chemistry Of Digitalis
( Originally Published 1921 )
My mental picture is this : The digitalis acts in a chemical way on the tissue of the heart very much as alkali acts on an acid mixture when you drop it in a little at a time. If you place some-litmus paper or other indicator in the test-tube and drop in the alkali solution, all of a sudden the mixture changes to blue, and then you know that you have your solution saturated. Now suppose some force was acting that had a tendency to change that solution back to acid; you would have to keep adding a little of the alkali right along to keep the reaction as it was, but if you added more alkali than is being, destroyed, you would reverse the process and get a caustic mixture. Now do not understand that the chemical action of the digitalis on the heart is acid or alkaline, but keep that illustration in mind to help you remember that in some way the digitalis modifies the chemistry of the heart-beat after a sufficient time has elapsed. This action has both a quantity element and a time element. For that reason digitalis is of no use as an emergency drug where you have not time to wait for the effect. But when you once get the effect, all of a sudden the chemistry of the heart is altered, and anything added over what is used up is unnecessary and harmful. Consequently the way to use digitalis is to give as much as is reasonable at first until the reaction of the heart occurs. Then stop the digitalis and give only as much as you believe is eliminated. If you go on with the original dosage you kill your patient.