258 Proceedings of Royal Society of Edinburgh. [sess. 
Note on the Passage of Water and other substances 
through Indiarubber Films. By R. A. Lundie, M.A., 
M.B., B.S.C., F.R.C.S.Ed. (With a Plate.) 
(Read December 20, 1897.) 
Indiarubber has come to be so nearly synonymous in popular 
language with waterproof that it seems almost as much of an imper- 
tinence 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 circum- 
stance was worth inquiring into. Is it simply due to stretching of 
the material, or is there an actual transudation through the india- 
rubber ? As I could get no answer to the question from people or 
from books, I determined to interrogate Nature for myself. 
By the kind permission of Professor Tait, I was enabled to per- 
form some experiments on the subject in the University Physical 
Laboratory. 
I took some of the thin indiarubber balloons used as playthings, 
filled them with water, secured the necks by a double tie with 
strong thread, and weighed them from time to time. Different 
sizes and different makes were used, but all gave very similar results. 
