134 CHEMICAL EQUILIBRIA 



C, nor the lecithin, Z, was consumed by the haemo- 

 lytic agent x. In this case Bordet is right : the 

 lecithin acts as a sensitiser. It is not only for 

 cobra poison that lecithin acts in this manner, but 

 even for other haemolytic agents, such as mercuric 

 chloride and acids. 



A very important group of antibodies from serum 

 are the precipitins, so called because they form a 

 precipitate with the substances injected in the veins. 

 In this manner lactoserum is prepared by the injec- 

 tion of skimmed milk (casein), and a serum against 

 egg-white by the injection of egg-white. These two 

 antibodies precipitate their specific antigens. 



The precipitins have evoked a very great interest. 

 They are used for deciding from which kind of animal 

 a blood -trace is derived. This method has been 

 developed especially in Germany by Uhlenhuth, 

 Wassermann, and others. It is mostly applied for 

 investigating if blood-spots on clothes or knives are 

 of human or animal origin, and has rendered great 

 services to justice. Another employment of pre- 

 cipitins is for determining the relationship of animals 

 or plants. The greatest merits in this field belong 

 to Nuttall, who has written a great monograph 

 on Blood Immunity and Blood Relationship (Cam- 

 bridge, 1904). 



Nuttall was the first to use a quantitative method 

 in this field by measuring the quantity of the pre- 

 cipitate collected in a capillary tube. As example, 

 the results of some experiments in which 010 cc. 

 of antiserum against human blood was mixed with 



