260 FERMENTS AND ANTIFERMENTS 



plus that of the placenta may show a deep violet-blue color when the 

 reaction is strongly positive, or a fainter blue when it is weakly positive. 

 If this dialysate is water clear or has a faint blue color, comparable to 

 the controls, the result is negative. If there is any doubt, the test 

 should be repeated. The negative control should be water clear or have 

 a faint tinge comparable to its control. The positive control should 

 show a deep violet-blue color. 



I generally control the result given by the shell containing tissue and 

 patient's serum by cleansing it thoroughly, boiling for a minute, and 

 testing it with egg-albumen solution or a serum, in case the reaction 

 was positive, to make sure that the shell has not allowed the passage of 

 serum, or with peptone solution, in case the reaction was negative, to 

 make sure that it was not thick enough to block the passage of peptones 

 and amino-acids. This procedure delays the report on a serum for an- 

 other twenty-four hours, but the greater accuracy obtained warrants the 

 delay. 



Readings should never be made by artificial light. Tubes should be 

 held against a wh\te background the better to appreciate the color 

 changes. 



A pinkish or brownish yellow discoloration has nothing to do with 

 the ninhydrin reaction. 



Sources of Error in the Dialyzation Method. There are many 

 sources of error, and until the technic has been improved sufficiently to 

 eliminate these, Abderhalden's directions should be followed minutely. 



1. The shells may become spoiled in time. They should not be 

 cleansed with rough brushes or boiled too long. They should be 

 cleansed at once after using, and tested every four weeks. If a wrong 

 diagnosis results, the shell should be retested at once. 



2. The placental tissue is an important source of error, due to the 

 fact that it contains blood. 



3. The serum should be fresh and free from hemoglobin and cor- 

 puscles. 



4. The controls on placenta alone and each serum alone are abso- 

 lutely necessary, as both may contain various substances capable of 

 reacting with ninhydrin and thus yielding false positive reactions. 



5. The water used should be distilled and sterile. The glassware 

 should be chemically clean and sterile, and the laboratory free from the 

 fumes of acids and alkalis. It is very important that absolutely the 

 same conditions should exist for the control tests as for the main test 

 itself. 



