REACTIONS BETWEEN ANTIBODIES 27 



the Lister Institute on mixtures of a lysin from the Bacillus 

 megatherium and its antitoxin. 1 He found that the poison 

 from innocuous mixtures was concentrated in the gelatin- 

 film, whereas the residue of the fluid exhibited antitoxic 

 properties. He therefore concludes that the binding of 

 this poison to its antibody is due to a " partially " revers- 

 ible process. This proof seems the more conclusive, as 

 Craw evidently worked under theoretical premises which 

 led him to seek for proof against the reversibility of the 

 process. 



The experiments resulted in the same manner, even if a 

 great excess of antilysin, one to three times the " neutral- 

 ising " quantity, were added. Craw had taken the precau- 

 tion to heat his mixtures for three hours at 37 C. and then 

 to let them stand one hour at 10 C., so that there is every 

 reason to believe that the reaction, which probably is very 

 similar to that of tetanolysin, had practically reached its 

 end. In the filtrate, Craw did not find a trace of the 

 poison when he worked with " neutral " or " over-neu- 

 tralised " solutions. 



Let us for a moment consider the ideas which led Craw 

 to suppose that the processes of binding between toxin 

 and antitoxin are not reversible. Toxins, and specially 

 antitoxins, are said to be colloids. Craw therefore supposes 

 the so-called solutions of antitoxins and the products of 

 their reactions with toxins to be in reality fine suspensions. 

 For this statement no evidence is adduced, but it seems as 

 if Craw regarded the lack of diffusibility as characteristic 

 of suspensions, and this may be conceded as being correct. 

 But since Craw supposes antitoxins to be non-diffusible, he 



1 T. A. Craw : Proc, Roy. Soc. t 76. 179 (1905). 



