CHEMICAL PHENOMENA IN LIFE 



not so. If we heat the mixture of antitoxin and 

 cytotoxin to nearly the temperature at which the 

 latter is destroyed by heat, we can reach a point 

 where the mixture again becomes toxic. We 

 get the impression that the antitoxin in the com- 

 pound has been sooner destroyed by heat than the 

 cytotoxin, and the latter has again become free and 

 effective. This most important experiment shows 

 us that both anti-substances enter into a com- 

 bination, analogous to that of chemical compounds. 

 Since we know that both substances are colloids, 

 we could suppose that colloid reactions are re- 

 sponsible for the phenomenon. Otherwise we 

 could think that the reaction is to be considered a 

 chemical combination of both substances. At 

 present there are many difficulties in the way of 

 giving a satisfactory explanation of the reaction. 

 Arrhenius drew a most instructive parallel between 

 the neutralisation of toxin and antitoxin, and the 

 neutralisation of a moderately strong alkali, such as 

 ammonia, with a weak acid, e.g. boric acid. Both 

 processes, indeed, have a great resemblance. 

 Ehrlich's ingenious hypothesis, well known as the 

 so-called Side Chain-Theory, culminates in the 

 supposition that the anti-substances represent 

 highly compound molecules with many atom- 

 groups, such as proteids possess. The neutralisa- 

 tion is done by binding two distinct groups. These 

 groups may be destroyed by heat, and both sub- 

 stances again set free. Possibly the two theories 

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