Page:Defensive Ferments of the Animal Organism (3rd edition).djvu/176

 not to spill any of the egg solution upon the exterior of the dialysing tube. Should this occur, the dialysate would incorrectly show a positive reaction for peptones, when, for instance, the biuret test is applied, since both albumens and peptones give this reaction. To avoid any chance of such an error, the dialysing tube, after having been filled, is closed at the top between the thumb and forefinger and well rinsed in running water. Then the tube is closed in the same manner half way down, and water is allowed

. 7.

to enter the upper part of the tube, so as to wash that part of the dialysing tube which, during the dialysing process, projects out of the dialysate and above the layer of toluol. By moving the thumb and forefinger towards the upper end of the tube we expel the water remaining after washing. All these manipulations have the following object:—

When filling the tube with albumen its interior, near the free edge, may easily come into contact with the pipette. Some of the albumen may adhere to the edge of the tube and dry up in time. At the