418 BACTERIOLOGICAL CHEMISTRY 



aud the blood group A polysaccharide give no reaction 

 with the two gum antisera. 



Antibodies 

 Our knowledge of the chemistry of antibodies is at 

 present rather vague. For the most part we only know 

 antibodies by the reactions which they give, and we have 

 but little insight into their chemical differentiation. As 

 we have already stated, they are produced as a result of 

 the injection of foreign colloidal substances into the 

 animal system. It has been conjectured that they are not 

 even new substances but merely an altered physical state 

 of the normal serum proteins . Practically all the evidence, 

 however, points to the fact that they are entities and 

 capable of a separate existence ; they can be removed, 

 either specifically by the corresponding antigen or by such 

 non-specific agents as kaolin or alumina, from the anti- 

 serum and then recovered from the complex by suitable 

 means . 



Composition of Antibodies. — That antibodies are pro- 

 tein in nature is shown by the fact that the specific 

 precipitates contain more protein than can be accounted 

 for by the antigen. This is particularly striking when 

 the antigen is a soluble specific polysaccharide, such as 

 that of Type I pneumococci, which itself contains no 

 protein. That the protein in these precipitates is not due 

 to non-specific adsorption is shown by an experiment in 

 which an antiserum was coupled with diazotised benzi- 

 dine-R-salt to give a bright -red dye ; the dyed antiserum 

 was used in specific and non-specific precipitin reactions, 

 the red colour appearing only in those precipitates in 

 which the antiserum was one of a homologous pair. 

 Again, bacteria or red blood corpuscles sensitised with an 

 antibody acquire a new isoelectric point and move in an 

 electric field as though they were coated with globulin. 

 Such systems, as well as toxin-antitoxin mixtures, con- 

 taining, say, an antibody prepared in a horse, if injected 



