274 pkesident's address — section l. 



of combining with the body cell and, for all practical purposes, 

 inert. Thus, according to Ehrlich's view, antitoxin consists of 

 numerous free receptors circulating in the blood and bod37 fluids 

 with specific affinity for toxin molecules. This "side-chain " 

 theory, with modifications, has been applied by Ehrlich to explain 

 thei production of the other types of antibody, agglutinins, 'pre- 

 cipitins, hemolysins, he, and it is obviously founded vipon a 

 supposed analogy taken from organic chemistry. Further, Ehilich 

 has suggested that the union of antigen and antibody (in the 

 simplest case toxin and antitoxin) is a chemical combination fol- 

 lowing the law of multiple proportions. This view has been made 

 the subject of acute controversy, and, with all due deference to 

 the genius of Ehrlich, it may be said that his views of this antigen- 

 antibody combination can no longer be accepted. 



Many attempts have l)een made to ascertain the exact chemical 

 constitution of anttljodies, but it is a matter of great difficulty 

 because of tlie impossibility of obtaining them in a state of purity. 

 As colloids they enter into physical, if not chemical, union with 

 other protein groups, and cannot be with certainty separated. It 

 is established that thev are precipitated with the globulins and, 

 in tlie casei of tetanus and diphtheria antitoxins, almost entirely 

 with the pseudo-globulin group. An ingenious method which has 

 been used in the attempt to obtain the antibodies pure is that of 

 adding toi a particular serum containing an antibody the proper 

 antigen, allowing a short time to elapse for combination, then 

 removing and carefully washing the antigen-antibody complex and 

 attempting to separate the two by the action of dilute acids and 

 alkalis. All tTiat ap^pears possible: to say at present is that the 

 antibodies are protein in nature and behave like colloids, i.e., are 

 not dialysable. 



What, then, is the nature of the antigen -antihody combin-ation ? 

 Her©, again, we may take first the simplest case, the union of 

 antitoxin and toxin. If this can be solved there is surely ©very 

 a, priori reason toi expect antigen-antibody combinations generally 

 to be subject to tlie one common theory. 



The first point which can be determined is that antitoxin acts 

 directly on toxin to' destroy its toxic powers, and not on the vulner- 

 able cells, to make them immune. One or two experiments which 

 prove this may be given. Fici77 has the power of agglutinating 

 red blood corpuscles, but if ricin is first mixed with antiricin (i.e., 

 the serum of an animal which has been immunized against ricin) 

 its agglutinating power is lost. If, however, red cells are mixed 

 first with antiricin serum, then washed free of it in saline and 

 submitted to the action of ricin, they are agglutinated. Again, 

 an old experiment of Martin and Cherry with snake venom showed 

 tha!. the toxin would pass throngh a porcelain filter impregnated 

 with gelatine, whilst aiitivenin sei"um would not. If venom and 

 antivenom serum were mixed together, and a sufficient interval 

 allowed to elapse, neither would pass the filter, for combination 

 had occurred. 



