Page:Defensive Ferments of the Animal Organism (3rd edition).djvu/177

 conclusion of the test some parts of this albumen may fall into the dialysate and pollute it. During the operation of cleansing the inside of the tubes, care must be taken to prevent water from entering the tubes. Before touching the tubes the hands should be thoroughly cleansed. The use of forceps is much recommended, and these must have wide, parallel, smooth arms.

The rinsed tubes are again put into Erlenmeyer flasks which contain 20 c.c. of sterile distilled water. The filling of the dialysation tubes must never be done in the same flasks in which it is intended to carry out the dialysation; something out of the pipette may too easily get into the flask. In order to prevent contamination the surrounding fluid, as well as the contents of the tubes, is covered with a layer of toluol about ½ cm. thick (fig. 7, p. 151). It is best to cover the flasks with watch glasses, unless one is prepared to use stoppered vessels. The dialysation is carried on at the temperature of the room, or, better still, in a closed space at a constant temperature—i.e., in an incubator.

After about sixteen hours—time is of no importance in this test, since the tubes are in this case merely tested for their permeability towards colloids—the dialysation is interrupted. The Erlenmeyer flasks, which should bear corresponding numbers, are placed in a row. By means of a pipette, which is