chap, xxii.] DIALYSIS. 261 



dialyser (a, Fig. 117) is then floated in a vessel con- 

 taining a considerable quantity of distilled water. The 

 crystalloids will readily pass through, 

 but colloids will be perfectly retained. 



Liebig described, years before, an 

 arrangement not dissimilar to this. " If 



O 



we tie moist paper over the open end 

 of a cylindrical tube, and, after pour- 

 ing in above the paper white of egg to 

 the height of a few lines, place that end of the tube 

 in boiling water, the albumen is- coagulated ; and 

 when the paper is removed, we have a tube closed 

 with an accurately-fitting plug of coagulated al- 

 bumen, which allows neither water nor brine to run 

 through. If the tube be now filled to one-half with 



O 



brine and immersed in pure water, the brine is seen 

 gradually to rise, and in three or four days it in- 

 creases by from a quarter to one-half of its volume, 

 exactly as if the tube had been closed with a very 

 thick membrane." * 



The dialyser affords a means of purifying colloidal 

 matter from crystalloids. The mixture requires only 

 to be placed in the dialyser on water, and the crystal- 

 loids are separated out. Albumen may be purified in 

 the same way. It was urged by Graham that the 

 method of dialysis could with advantage be applied in 

 medico-legal cases to- the separation of such crystal- 

 loids as arsenious acid from organic solutions, such 

 as the contents of the stomach, blood, etc. Strychnine 

 and tartar emetic were separated in the same way. 



While the dialyser shows albumen to be very 

 feebly diffusible, peptones are largely so. 



Mechanism of absorption. There can be no 

 doubt that osmosis plays an important part in ab- 

 sorption, even though it may not explain the whole 

 of the process. Let the conditions be observed. In 

 * Liebig " On the Motion of the Juices in the Animal Body," 1848. 



