196 A MANUAL OF BACTERIOLOGY 



on the addition of a small amount of antitoxin to toxin there is 

 no decrease in toxicity (as noted by Ehrlich and attributed by 

 him to the presence of toxoid), as there should be, and Arrhenius 

 was thus forced to the conclusion that a second substance, epi- 

 toxonoid, is present with the toxin in diphtheria toxin. Craw 

 denied that the toxin-antitoxin reaction is reversible, as antitoxin 

 must be regarded as a colloid (and is not in true solution), the 

 mixture is therefore heterogeneous, not homogeneous, and the 

 chemical law of mass action is not applicable. 



On the other hand, Craw maintained that the phenomena of 

 the toxin-antitoxin reaction, including the Danysz effect, have 

 their counterpart in adsorption phenomena, such as occur in the 

 staining of paper, porcelain, etc., with anilin dyes, in the " adsorp- 

 tion " of substances by colloids, etc., 1 and this view is supported 

 by Bordet, Gengou and H. R. Dean. Thus, when solutions of 

 arsenious acid are shaken up with colloidal ferric hydroxide, a 

 portion of the arsenic is taken up by the ferric hydroxide and a 

 portion remains in solution. Moreover, proportionately more 

 arsenious oxide is taken up by ferric hydroxide from dilute than 

 from concentrated solutions ; this has its counterpart in agglu- 

 tination. Again, when an antitoxin is added to a toxin in just 

 sufficient amount to produce a non-toxic solution, the amount of 

 toxin which must then be added to constitute a fatal dose is 

 greater than the minimum lethal dose without antitoxin. This 

 is also found to be the case with ferric hydroxide and arsenious 

 acid ; if ferric hydroxide and arsenious acid are mixed so as to 

 form just a non-toxic mixture, the amount of arsenious acid which 

 must then be added to render the mixture toxic is greater than 

 the toxic dose of arsenious acid. 2 



If pieces of filter-paper be placed in a dilute solution of stain at 

 sufficiently long intervals, the pieces first immersed will become 

 coloured while those last immersed will remain colourless. On 

 the other hand, if all the pieces be simultaneously placed in the 

 solution they all become coloured to the same degree. This is 

 exactly comparable to the Danysz effect. All the phenomena of 

 the toxin -antitoxin reaction seem best explained on the adsorp- 



1 " Adsorption " is physical in nature and mainly due to surface condensa- 

 tion. 



2 See Findlay, Physical Chemistry and its Applications in Medical and 

 Biological Science, 1905. 



