Page:Defensive Ferments of the Animal Organism (3rd edition).djvu/213

 following: About five to ten times more of the substrate 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 1 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 testing 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—0.5 gr. of 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 misunderstood. An organ must have been very unsatisfactorily prepared, if the 20 c.c. of the dialysate contain such a quantity of substances reacting with ninhydrin that the reaction, after being conducted in the usual way, gives positive results.