264 INFECTION AND IMMUNITY 



Modern theories of solution maintain that substances in solution 

 are broken up into their atoms or atom-groups, known as ions. Thus, 

 NaCl in solution would be "dissociated" into its Na ion and its 

 Cl ion, the completeness of the dissociation depending upon the 

 concentration of the solution. A solution of NaCl, therefore, con- 

 tains, according to this view, three substances, NaCl undissociated 

 and free ions of Na and Cl, the relative quantities of the three 

 present in any given solution being calculable, and depend upon 

 a law known as the law of mass-action of Guldberg and Waage. 

 These free ions are the elements, "therefore, which are active in the 

 formation of further chemical combination. When a strong acid, 

 in solution, acts upon a base, say HC1 upon ammonia (NH 3 ), strong 

 acid having the property of quite complete dissociation in relatively 

 concentrated solutions, little or no ammonia would remain unbound. 

 A weak acid, like boric acid, however, not being as completely 

 dissociated, would leave some ammonia uncombined even after more 

 quantitatively sufficient bone acid had been added. Arrhenius and 

 Madsen, on the basis of careful researches into the reaction between 

 tetanolysin and its antibody, believe that toxin and antitoxin possess 

 weak chemical avidity for each other, their interaction being com- 

 parable to that taking place between a weak acid and a base. Toxin- 

 antitoxin solutions, therefore, would contain the neutral compound, 

 but at the same time uncombined toxin and antitoxin. The 

 qualities which Ehrlich ascribes to toxon, they believe, are 

 due to the: unbound toxin present in such mixtures. In careful 

 studies in which they inhibited the hemolytic action of ammonia by 

 gradual addition of boric acid, they were able to show complete 

 parallelism between the conditions governing this neutralization and 

 those concerned in their tetanus experiments. Their explanation has 

 the advantage of great simplicity over that of Ehrlich 's and also 

 the fact that it takes into account the laws of dissociation which 

 always takes place in solutions in which the union 01 two substances 

 occurs. We cannot enter into the matter at greater length in this 

 place, and must refer the reader to more extensive works on im- 

 munity. 21 Objections to the ideas of Arrhenius and Madsen have 

 been brought forward by Nernst, Bordet and others, largely on the 

 basis that toxin-antitoxin are probably colloidal in nature, and that 

 the laws of dissociation in colloidal reactions are not, as yet, clear. 



21 See Zinsser, Infection and Kesistanee, MacMillan & Co., New York, 1917; 

 Bordet, Immunite, Masson, Paris, 1920. 



