This is one of a number of apparatus which were designed by the writer about seventeen years ago for the purpose of applying heat and cold at graduated temperatures to different parts of the body. They include, besides the water-cap, a spinal bag (which has been of great use in the treatment of various diseases of the spinal cord), a chest and abdominal bag, a uterine bag, and a throat bag. A description of them, particularly of the chest one, was published in a serial paper in the “British Medical Journal” for November and December, 1871, and in the “Glasgow Medical Journal” previously. I have added this note to prevent possible misapprehension, as there are now other apparatus, metallic as well as India-rubber, in use, constructed on the same principle, but all of them have been introduced since the period referred to.