184 PERFORMANCE OF THE EXPERIMENT 



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 uncon- 

 ditionally positive. 17 If, on the contrary, the sample, 

 organ + serum, has evaporated more, then we are con- 

 fronted with the possibility that the stronger concen- 

 tration 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 



17 If the reaction is very weak, one may try to make it 

 stronger in the following manner : To each of the cooled solu- 

 tions dialysate from the experiment serum alone, and serum 

 + substrate one again adds o'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 com- 

 parison with the dialysate of the serum only. Our present 

 experience is still too small to enable us to recommend this 

 process for general use. 



