THE DIALYSATION PROCESS 147 



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, sub- 

 stances 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 proteolvtic 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 



