2OO SOURCES OF ERROR (IN THE PROCESS) 



which has been so strongly diluted, that 5 c.c. of the 

 solution just fails to show any coloration with i 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 i 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 delimita- 

 tion. 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 



