ANTIGENS, HAPTENS, ANTIBODIES, ETC. 417 



amino groups of lysine. The antisenini prepared agaiiLst 

 this antigen is specific for histamine and gives cross 

 reactions witli hist amine -azoproteins. Guinea-pigs im- 

 munised by injection of the histamine antigen were 

 protected against the physiological effects of histamine. 



In contrast to the effect of isocyanates Landsteiner 

 found that when the amino groups of proteins are con- 

 densed with formaldehyde with introduction of a 

 methylene group, 



R— NHa + HCHO > R— N = CH2 + HgO, 



there is no apparent change in the specificity of the 

 proteins, which behave immunologically exactly as the 

 untreated proteins . This fact is made use of in preparing 

 anti-toxins ; the toxin is converted to the toxoid by the 

 action of formaldehyde. The toxoid, although non-toxic, 

 is still capable of provoking the formation of antibodies 

 which react specifically with the original toxin. 



It was mentioned on p. 362 that the somatic antigens 

 of Shigella dysenterice and Eherthella typhosa could be 

 broken down by the action of 90 per cent, phenol into a 

 polysaccharide hapten and an antigenic protein, and that 

 the two components could be recombined by solution in 

 formamide and precipitation of the complex by alcohol. 

 The protein is also capable of being coupled with other 

 polysaccharides in the same way to give antigenic com- 

 plexes. Thus with agar, gum acacia, cherry gum, and 

 the blood group A specific polysaccharide (isolated from 

 commercial pepsin, peptone or gastric mucin) antigens 

 are formed in which the specificity is determined by the 

 polysaccharide moiety. Gum acacia gives no precipitin 

 reaction with cherry gum antiserum, although cherry 

 gum gives a weak reaction with gum acacia antiserum. 

 Other polysaccharides such as kanten (a degradation 

 product of agar), gum tragacanth, hyaluronic acid, the 

 specific polysaccharides of Types I and II pneumococci 



