The salts of sodium resemble potassium in their action on the alimentary tract, but they are much more slowly absorbed, and much less diffusible; therefore considerable amounts may reach the small intestine and there act as saline purgatives.
The proteolvtic enzymes, or those which digest proteids, are usually divided into two groups, one which breaks down ordinary proteids into diffusible bodies, known as peptones, which are themselves proteid in character.
Ether is thus the type of a rapidly diffusible stimulant.
The soluble soaps which are probably conveyed by the blood will be quickly taken up by such cells, synthetized into neutral fats, and stored in a non-diffusible form till required.
Again the two classes of substances mentioned above were found to be distinguished, and Graham called the slowly diffusible non-crystalline bodies colloids, in contrast to the quickly diffusible crystalloids.