SOURCES OF ERROR (iN THE PROCESS) 193 



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 



