Page:Defensive Ferments of the Animal Organism (3rd edition).djvu/218

 ninhydrin. It is obvious, for the reasons mentioned, that exactly the same quantity of serum must be added to the organ, as has been used for the control test with serum alone. We must never, on the strength of the fact that the test with the serum alone gives a positive reaction, jump to the conclusion that, during the test, proteins have been decomposed in the serum. The substances producing this reaction were present from the beginning. If the reaction with serum alone turns out negative, then it simply means that the dialysate contains those compounds, which react with ninhydrin, in a state of concentration insufficient to produce a coloration; and this is the only conclusion we are entitled to draw from the result. It certainly does not indicate that there are no such compounds present. If one concentrates a dialysate of this kind, it eventually gives a positive reaction.

We therefore arrive at the fact, that we can only determine whether there are sufficient compounds present to give the coloration, but not what the quantities actually are. If, however, the following conditions are complied with, then this circumstance offers no difficulties. The organ must be absolutely free from substances, reacting with ninhydrin, which can be boiled out and so passed over to the filtrate. When the tubes are rinsed, no water should be allowed to enter them. The organ must be perfectly dried, 13