Celluloid shirt collar
This collar was worn by a Boston streetcar motorman who was subject to attacks of dizziness and loss of consciousness on the job. Upon examination at Massachusetts General Hospital, it was determined that when the motorman turned his head, his stiff shirt collar pressed against the right carotid sinus, triggering a fainting attack. "Pulse and blood pressure measurements were made with the patient turning his head from side to side while wearing one of his celluloid collars. These movements caused pressure on the carotid sinuses, and resulted in slight slowing of the heart rate, fall in blood pressure as much as 40mm. Hg systolic, sometimes dizziness, but not fainting. The patient was advised to wear a soft collar, which he has done for the past month. In that time has had no more attacks of dizziness or fainting."
Dr. Soma Weiss (1899-1942) described this case in his article, "Carotid sinus reflex in health and disease," published in Medicine, v. 12 (1933).