ANTIBODIES 117 



loids is therefore of importance in view of the 

 modern teachings respecting immunity. 



The living organism produces curative or protec- 

 tive agents in the blood, antigens and antibodies. 

 The antigens are substances which give rise to the 

 antibodies. Their chemical composition is un- 

 known, but they have a colloidal constitution. The 

 study of these substances was begun with the dis- 

 covery of antitoxins by von Behring. 



The antibodies, such as antitoxin and anti- 

 bacterial substances, are monotropic, i.e. " they 

 are so to speak charmed bullets which strike only 

 those objects for whose destruction they have been 

 produced by the organism, and they are directed 

 against bacteria or against the products of their 

 metabolism (toxins) which cause disease."* The 

 cause of this specificity is in Ehrlich's opinion the 

 effect of the chemical relation which exists between 

 the infective body and the antibody. They fit one 

 another as a key fits a lock. The colloid nature and 

 chemical reactive power of the immune substance 

 do not exclude one another ;f for colloids possess 

 certain groups of atoms which render them capable 

 of reactions of a synthetic nature. ' The condition 

 for this action is the presence of two groups, whose 

 chemical relationship is of the closest and whose 

 interaction is therefore a condition of their union. 

 This action as to union is the basis of my side-chain 

 theory."J 



* Ehrlich : "The Harben Lectures," Jour. Roy. Inst. Pub. 

 Health, 1907, p. 323. 



f Loc. cit. 



+ Ehrlich: "The Harben Lectures," Jour. Hoy. Inst. Pub. 

 Health, p. 324, 



