274 FERMENTS AND ANTIFERMENTS 



held against a white 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. 



THE OPTICAL METHOD 



In the dialyzation method, we establish the transformation of a 

 colloid into a diffusible crystalloid; in the optical method we start, 

 for purely technical reasons, not with the whole protein molecule, but 

 with a peptone prepared of placental protein. The unsplit protein it- 

 self cannot be used, as this will interfere with the determination of the 

 rotation of the mixture of substratum plus serum. Further, in such 

 mixtures precipitation may occur and render the readings difficult. 

 Instead, we transform the protein into peptone, and observe the final 

 changes in the tube of the polariscope. 



Placental Peptone. This requires considerable care in its prepara- 

 tion. Placental peptone may be purchased of the Hochst Farbwerke, 

 and is expensive. Each specimen should be tested and its rotation de- 

 termined, as otherwise uncertain and unreliable results may be secured. 

 According to Abderhalden, a peptone may be prepared as follows: 



