128 APPLIED IMMUNOLOGY 



sorbed in reactions stronger than this. We believe 

 that this method of designation conveys more informa- 

 tion as a rule to the clinician than the plus signs. We 

 are indebted to Dr. John L. Laird for the principles 

 we follow in quantitative determination (Pa. Med, 

 Jour., 1911-12, XV, 97-102). For those who wish to 

 measure the percentage of haemolysis more exactly, the 

 Duboscq colorimeter may be used according to a 

 method described by one of us (Ivy, Jou7\ Amer. Med. 

 Assn., Aug. 10, 1912, p. 432). We regard this accu- 

 rate measurement as seldom called for, yet the method 

 may be fomid useful to those who are in the habit of 

 guessing the percentage of haemolysis in giving their 

 results. 



The sera that have been tested can be preserved 

 and used as positive and negative controls in future 

 reactions, provided they are reinactivated by heating 

 before subsequent tests are made. 



The table (Plate II) illustrates the performance 

 of the test on an unknown serum, with positive and 

 negative controls. 



Modifications of the Wassermann Reaction 



Each worker is apt to vary from the original 

 technic in minor details to suit his own convenience in 

 the performance of the Wassermann reaction. These 

 slight modifications are in no way to be regarded as 

 radical changes in the reaction. By the original Was- 



