Methods in Use.
I.—The Dialysation Process.
The principle of the method: Albumen being a colloid does not diffuse through animal membranes, while on the other hand peptones—the first products of its decomposition—are diffusible. If we put albumen in a dialysing tube and place the latter in water, no albumen appears in the surrounding fluid even after a considerable time. If, however, substances such as pepsin and hydrochloric acid are added to the albumen in the tube, we can soon trace, in the water surrounding the tube, substances which are produced from the decomposition of the albumen. These substances are the so-called peptones and some other simpler products of decomposition. If we desire to test any liquid to ascertain whether it contains any proteolytic—i.e., albumen-decomposing—ferments, we place it in a dialysing tube together with albumen, and note whether peptones appear in the liquid surrounding the dialysing tube. If none are present, we may be sure that the tested liquid
