SERUM THERAPY HI 



ways been as satisfactory as those obtained with 

 specific antitoxic sera. The chief reasons for 

 failure are: (1) It is not possible to accumulate 

 antibodies in the sera of animals immunized 

 against bacteria in a concentration as efficient 

 as the antibodies in sera of animals immunized 

 against toxins; (2) it has been impossible to ad- 

 just the dosage by any accurate unit and the 

 doses which have generally been used have 

 doubtless been too small to produce the desired 

 favorable results; (3) because of the lack of 

 appropriate tests for standardization, inert 

 sera probably have been placed on the mar- 

 ket. Up to the present time, no universally ac- 

 cepted unit of immunity has been applied to the 

 antibacterial sera. However, in our labora- 

 tories, the therapeutic activity and antibody 

 content of the serum obtained from each im- 

 munized horse are determined as accurately as 

 possible by certain laboratory methods, includ- 

 ing the complement fixation test and the esti- 

 mation of the opsonic index. (See Part III). 

 These tests prevent an inert serum from at any 

 time being marketed. Without such tests, sera 

 without any value whatever might be and prob- 

 ably have been marketed, and this doubtless ac- 



