Page:Defensive Ferments of the Animal Organism (3rd edition).djvu/183

 transfer the dialysates into the test-tubes by means of one pipette. It is essential to have at one's disposal for the actual tests as many different pipettes, graduated to 10 c.c., as there are dialysates to be handled. The test-tubes must also be absolutely clean and dry, and they must be of exactly the same width. Pouring the dialysates into the test-tubes is not admissible, because the toluol may easily spoil the reaction, chiefly by preventing satisfactory boiling.

In detail one proceeds as follows: As before, the pipette, closed at the top with the finger, is passed through the toluol layer, and 10 c.c. of the dialysate are withdrawn. The pipette is kept closed when passing through the toluol layer, in order to prevent any toluol from entering it. After transferring 10 c.c. of all the dialysates into the test-tubes, using separate pipettes for each, we add to each test exactly 0.2 c.c. of an accurately prepared 1 per cent. solution of ninhydrin.

For accurate measurements a capillary pipette of 1 c.c. is used. The ninhydrin solution is prepared as follows: ninhydrin is usually sold in 0.1-gr. packets, and this quantity is shaken out of the tube into a measuring flask marked to 10 c.c. The tube is best emptied by tapping it against the inside of the mouth of the measure, though it is not possible by this means to transfer the whole of the 0.1 gr. of ninhvdrin into the measure. The rest of the