18 VACCINE AND SEKUM THERAPY 



amount. In a general way these *' normal agglu- 

 tinins " have the same nature as the immune agglu- 

 tinins, and their presence is probably due to the 

 presence of various micro-organisms parasitic on 

 animals. Agglutinins may be produced in the sera 

 of animals by the introduction of bacteria, subcu- 

 taneously and intravenously. As a rule they appear 

 in the blood three to six days after the introduction 

 of the bacteria. 



Precipitins. — The precipitins, like the agglutinins, 

 may be inactivated by heating to from 60° to 70° C, 

 and cannot be reactivated by the addition of normal 

 serum or by any other known method. 



Sj^ecificity. — The specificity of precipitins is a 

 question of very great importance, since these bodies 

 have been used extensively for the differentiation 

 of animal proteids. This specificity of precipitins 

 has been used for forensic purposes by Wassermann, 

 Uhlenhuth, and others, to distinguish the blood of 

 one species of animal from another. Thus, blood- 

 stains, dissolved out in normal saline solution, could 

 be recognised by this reaction as originating from 

 man or from an animal, even after months of drying. 

 Precipitins have not been so far found in normal 

 sera. 



Multiplicity of Amboceptors. — As has been al- 

 ready shown, normal sera possess moderate bacterio- 

 lytic power, which can be destroyed by heating. 

 Since such inactivated normal serum can be reacti- 

 vated by the addition of fresh serum, it is plain that 



