From Dental Cosmos, http://quod.lib.umich.edu/d/dencos/acf8385.0032.001/504:166?rgn=full+text;view=image
Dr. Joseph C. Barnum. At the residence of his father, in Monticello, N. Y., April 18, 1890, of Bright's disease, Joseph Clowes Barnum, DDS, in the forty-third year of his age. The deceased was the son of George W. and Caroline G. Barnum, and a brother of the late Sanford C. Barnum, DDS, so well known to the profession as the inventor of the "rubber-dam." He never married, and of his immediate relatives his father alone survives him.
Dr. Barnum graduated from the Pennsylvania College of Dental Surgery in 1871, and began the practice of his profession at Monticello in the same year; he afterward practiced in Brooklyn, NY, for two years, but returned to Monticello in 1877, and continued practicing there until his death.
He was a man of unusual mental abilities, and was very thorough and successful in the practice of dentistry.
From the Republican Watchman, Monticello, NY, April 25, 1890: Dr. Joseph C. Barnum died at the residence of his father in this villiage on Friday, April 18th. His age was about 43 years. For several years Dr. Barnum has practiced dentistry here, and was considered a very successful practitioner. His oldest brother, Dr. Sanford Barnum, who died four or five years ago, was considered one of the most skillful men in his profession in the country. He was the inventor of the celebrated "Rubber Dam" appliance, now in use by every dentist of repute. Dr. Joseph Barnum, after studying and practicing with his brother, graduated at a dental college and established himself to his profession with such assiduity as to become a recluse. Never showing himself outside of his office, or on the street, during the daytime. This sedestary and close habit undoubtedly aided in shortening his life. The disease which terminated his career was Bright's disease of the kidneys.
His funeral was on Monday forenoon, and was private. His father George W. Barnum, is now lying in an extremely critical condition, with no prospects of recovery. His condition is so precarious that we are informed he was kept in ignorance of his son's death.
Mr. Barnum, who is one of the wealthiest men in our village, has survived all his family. His wife, whose death occurred some five or six years ago, has been followed to the tomb by his two sons within that time, and he still lingers on the earth, "the last of his line."
He died of Bright's Disease.