240 Wisconsin Academy of Sciences , Arts and Letters . 
that whether the solid will pass through the membrane or not 
depends on the nature of the solid, the membrane and the 
liquid employed. Furthermore, if the substance composing the 
solid does make its way through the septum, the fact as to 
whether the action is accompanied with an accumulation of 
liquid on that side of the septum occupied by the solid or not 
is clearly determined by the rate with which the solution formed 
is absorbed by the membrane (which is determined by the 
mutual attraction or affinity of the saturated solution and the 
membrane for each other) and also by the rate with which the 
pure solvent is imbibed from the other side. 
Now it is well known that camphor dissolves very readily in 
hydrocarbons and consequently has considerable affinity for 
rubber, and we should, therefore, expect it to pass through the 
latter when it is employed as an osmotic membrane. An alco¬ 
holic solution of camphor is more readily imbibed by rubber 
than is pure alcohol, and so it occasions no surprise when in No. 
42 we find the block of camphor slowly making its way through 
the rubber septum into the alcohol, and without the appearance 
of liquid on the side occupied by the camphor. The action is 
slow because alcohol is not imbibed rapidly or copiously and 
because the septum holds on to the strong camphor solution 
very tenaciously, so that only a small portion of the camphor 
thus saturating the rubber is washed out of the latter by the 
alcohol on the other side. 
When the same experiment is performed using a hydrocarbon 
as the liquid instead of alcohol, Nos. 43 and 44, the action goes 
on very much more rapidly on account of the great affinity be¬ 
tween rubber and the hydrocarbon or a camphor solution in a 
hydrocarbon. The strong camphor solution is so greedily ab¬ 
sorbed by the rubber that but little liquid appears on the upper 
side of the membrane while the solid camphor lasts, and it is 
as though the solid camphor were passing through the rubber 
septum by mere contact with it. The process reminds one 
strikingly of the manner in which solid food placed in the ali¬ 
mentary canal is digested and absorbed. Here the presence of 
the food in contact with the walls of the tract excites the flow 
of the digestive juices toward the solids, the latter are acted 
