This Thesis has been conducted essentially with a view to investigate the statisticsof cardiac paralysis in Diphtheria, so as to include all the interesting and important points: and also to ascertain the particular part which the heart itself plays in this condition. I hope that as regards the heart, to be able to show that there are very definite and grave pathological conditions in the heart muscle, etc., and which seem to be always present in this form of cardiac paralysis. As the investigations of cardiac paralysis statistics meant going over the whole of the cases of diphtheria in the case books of the hospital, I determined afterwards to do all the statistics of postdiphtheritic paralysis.