Permeability 149 
The observations of Chabry (1888) show that the course of 
diffusion of an electrolyte through a dead animal tissue is similar 
to its diffusion through a gel. Prismatic pieces of hyaline cartilage 
stained with orcein were fitted into a tube and any space between 
the tissue and the tube were filled with a transparent oil. The 
penetration of acid into the tissue was then followed by the indicator 
method in the same way as in the case of a gel, and it was found that 
% 
the consequence of Fick’s law, that —r = constant, held in this case 
yt 
as well as in the cases of diffusion in water and in gels. The value of 
the constant was however found to be considerably less than with 
diffusion into a gel. 
The diffusion of crystalloids through colloidal systems such as 
gels and dead organic tissue apparently proceeds in the same way 
as through water, although less rapidly. But the diffusion of colloids 
differs strikingly in a simple liquid and in a colloidal system. It is 
well known that Graham drew the fundamental distinction between 
colloids and crystalloids on account of the non-diffusibility of 
the former through membranes of parchment and other colloidal 
materials, while crystalloids diffused readily through such mem¬ 
branes. The diffusibility or non-diffusibility of a substance or group 
of substances through membranes is however generally not an 
absolute property of the membrane; it is a matter of degree. Thus 
colloidal membranes which are permeable to crystalloids do not let 
them all through equally readily. This is a matter of obviously great 
importance in relation to permeability of living tissue and requires 
to be considered in some detail; it therefore forms the subject of 
the next chapter. 
(To be continued.) 
