reaction. It may sometimes happen that, for instance, the dialysate of the serum gives a negative reaction, while serum + organ shows a slight violet coloration. If both samples have been boiled equally according to the directions, then both will have evaporated equally, and in this case the slightest coloration may be considered as unconditionally positive.[1] If, on the contrary, the sample, organ + serum, has evaporated more, then we are confronted with the possibility that the stronger concentration is the cause of the coloration. In spite of the presence of absolutely equal quantities of substances, capable of reacting with ninhydrin, in the dialysate of the serum and that of the sample serum + organ, a higher concentration has been obtained owing to stronger evaporation. If it is impossible to effect even boiling by any other means, then it is necessary to resort to a water bath. The samples to be compared are placed in a stand, and immersed in a water bath. The boiling must be continued longer than when heating in an open flame, but two to three minutes are
- ↑ If the reaction is very weak, one may try to make it stronger in the following manner: To each of the cooled solutions—dialysate from the experiment serum alone, and serum + substrate one again adds 0.2 c.c. of the ninhydrin solution, and boils for one minute. The reaction then often becomes stronger. Obviously we must in this case, too, make a comparison with the dialysate of the serum only. Our present experience is still too small to enable us to recommend this process for general use.
