Page:Defensive Ferments of the Animal Organism (3rd edition).djvu/187

 intensity of the blue coloration is made in each case. It is soon found that a particular intensity prevails. All the tests which show a greater or smaller intensity than this are carefully noted, and the tubes from which the dialysates in question were obtained are rejected. In this case, too, it is necessary to be very accurate, otherwise the actual experiments may easily lead to deceptive results. Thus it may happen that serum alone, and serum added to a given organ, contain diffusible compounds which react with ninhydrin with precisely equal difficulty; yet on testing the dialysate in the experiment serum + organ, we may get a positive reaction, because the tube was more permeable to decomposites of albumen than the tube used as a control.

The tubes that are equally permeable in this respect are now carefully rinsed, then plunged into boiling water for thirty seconds, and finally brought into a sterilized flask. Sterilized water is added, together with an equal quantity of toluol, the fluid being calculated to fill the flask exactly. The tubes are now ready for use. They are taken out of the flask with sterilized forceps and must, if possible, not come into any contact with the fingers during all the manipulations.

Preparation of the Substrates (Organs).—As material for these tests we use either an albuminous body or else a mixture of these bodies—e.g., an organ. The