ON THE MECHANISM OF THE PHYSIOLOGICAL ACTION OF THE CATHARTICS BY JOHN BRUCE MacCALLUM Late Assistant Professor of Physiology in the University of California BERKELEY THE UNIVERSITY PRESS 1906 JOHN BRUCE MACCALLUM. The following pamphlet was completed only a few days prior to the death of the author, which occurred on the sixth of April, nineteen hundred and six. Through his death Physiology was robbed of one of its most brilliant young investigators. John Bruce MacCallum was born in Dunnville, Canada, on the eighth day of June, eighteen hundred and seventy-six. Through the influence of his father, Dr. G. H. MacCallum, now Superintendent of the State Asylum at London, Ontario, his interest in the natural sciences was early aroused and during his college career at the University of Toronto as much of his time as possible was devoted to these subjects, but chiefly to biology. After his graduation in 1896 he entered the Medical School of Johns Hopkins University. Under the influence of Professor Mall he undertook during his first medical year an investigation on the histogenesis of the cells of the heart-muscle, and it was characteristic of him that he began his work in pathological anatomy also with an original investigation. During the third year of his medical course he again prepared several anatomical papers and at the same time assumed the burden of the proof reading and of preparing the index of Barker’s book on Neurology. It was during this year, 1898-1899, that the first symptoms of the disease appeared which was to cut short the life of this talented, indefatigable worker. From this time on he was constantly handicapped in his work by the struggle against illness. After his graduation in medicine in nineteen hundred he returned to Baltimore as assistant of Professor Mall. In nineteen hundred and one he went to Leipzig to work in the laboratory of His, but his old enemy again interrupted his work, this time attacking him in the form of an affection of the apex of the lungs. He returned home as soon as sufficiently recovered to bear the journey, and upon the advice of Dr. Osler he spent the winter in Jamaica. During this period he translated and edited Szymonowicz’s histology into English.