l88 PERFORMANCE OF THE EXPERIMENT 



following : About five to ten times more of the sub- 

 strate than has been used for the test is taken together 

 with 5 c.c. of water, and the whole is dialysed in an 

 incubator for sixteen hours, against 20 c.c. of distilled 

 water. Then the dialysate is evaporated on the water 

 bath to 5 c.c., and the latter is boiled in the usual way 

 with i c.c. of ninhydrin solution. The solution must 

 remain absolutely colourless. According to my own 

 experience this test always results negatively, when 

 the substrates have been prepared in accordance with 

 the directions. It is only necessary for the first test- 

 ing of the organ, and is carried out if doubts arise 

 as to the suitability of the latter. As the same organ 

 is always used over and over again for experiments 

 in which no decomposition is expected, we have a 

 concurrent control over the suitability of the organ. 

 Should errors occur in these experiments, then the 

 dialysing tubes are immediately tested, as well as the 

 organ, in the manner laid down. The statement that 

 for the control experiment organ alone was used- 

 '5 g r - f the organ and that 10 c.c. of the dialysate 

 have given a negative result, always proves that the 

 principles of the whole method have been misunder- 

 stood. An organ must have been very unsatis- 

 factorily prepared, if the 20 c.c. of the dialysate con- 

 tain such a quantity of substances reacting with 

 ninhydrin that the reaction, after being conducted in 

 the usual way, gives positive results. 



