Indiarubber has come to be so nearly synonymous in popular language with waterproof that it seems almost as much of an impertinence to inquire whether it really is so, as it would be to ask whether lead is heavy or iron strong. The question, however, came before me in a practical shape; and I have made out some facts, in attempting to answer it, which may be of interest.

A water-bed is simply a hollow indiarubber mattress, capable of being filled with water and secured by metal screws. Such beds are largely used in the treatment of paralysed and feeble patients; and it is well known to nurses and others who have much to do with them that they need every now and then to be filled up in order to keep them comfortable. I first became acquainted with this fact in the course of medical work at the Longmore Hospital, where there are always many of them in use. Every three months or so a considerable quantity of water needs to be added to each of them, because it becomes so slack that the patient sinks through the cushion of fluid and rests on the solid mattress below, at the points where pressure is greatest. It seemed to me that this circumstance was worth inquiring into. Is it simply due to stretching of the material, or is there an actual transudation through the indiarubber? As I could get no answer to the question from people or from books, I determined to interrogate Nature for myself.