which has been so strongly diluted, that 5 c.c. of the solution just fails to show any coloration with 1 c.c. of ninhydrin solution. 2.5 c.c. of this solution were then added to 2.5 c.c. of the filtrate obtained from the water in which the organ was boiled, and 2 c.c. of the ninhydrin solution were added to this. The mixture was boiled in the usual way for one minute, and the reaction remained negative. It would always have been possible for the limital value to be attained by means of additions. Further, a volume of 10 c.c. was reduced to 5 c.c. After the addition of 1 c.c., and later of 2 c.c. of the ninhydrin solution, no coloration appeared.
Finally, we may once more insist on the fact that an organ containing blood frequently fails to act, even when it fully complies with the conditions with reference to the water, in which the organ has been boiled (see pp. 164-168).
A desire has often been expressed, that we might have a special colour-scale for estimating the results of the ninhydrin reaction, with a view to recording the strengths of the reaction in a generally equivalent manner; but this cannot well be effected, because the ninhydrin reaction does not allow of sharp delimitation. With experience, each observer will soon be able to judge whether the reaction is strong, medium, slight, or very slight. Besides, we must not lay too much stress upon the intensity of the reaction. It is
