A little over a year ago, we found that one single injection of 0.2 c.c. of adrenalin causes, in many cases, the appearance of a myocarditic lesion in rabbits,1and that the injection of small doses of spartein (0.012 gm. per kilogram) or caffein (0.025 gm. per kilogram), followed by the injection of a small quantity of adrenalin (0.2 c.c. of a 1 to 1,000 solution), produced macroscopic changes in the hearts of 60 per cent. of the animals and microscopic changes in almost all cases. We concluded therefrom that the typical effect of the intravenous injection of adrenalin was a cardiac, and not an aortic lesion. I. MYOCARDITIC LESION PRODUCED BY ONE INJECTION OF ADRENALIN This method of producing a myocarditic lesion enabled us to study the sequence of the changes which resulted from these injections, by examining the animals at various periods after the single