516 THE RELATION OF COLLOIDS AND LIPOIDS TO IMMUNITY 



are, in the final analysis, products of cellular activity, and therefore 

 derived from colloidal solutions. 



1. Antitoxins. The side-chain theory of Ehrlich was first applied 

 in explanation of the principles of immunity as affording an explanation 

 of the action of toxins, the formation of antitoxin, and the interaction 

 between these. Ehrlich has placed the various phenomena of immunity 

 upon a chemical basis, bringing forward new theories to explain the 

 various discrepancies that were found. For example, it was soon found 

 that both toxin and antitoxin were unstable, and that neutralization of 

 a toxin by the addition of antitoxin was not a simple process, like the 

 neutralization of an acid by an alkali, but, on the contrary, was likely to 

 be exceedingly complicated. This was explained as being due to the 

 degeneration of toxin into various toxoids, which were able to neutralize 

 antitoxin without being in themselves toxic when in a free state. They 

 were likewise found to have a greater affinity for antitoxin than the toxin 

 itself, so that when a toxin was tested and its toxicity determined, it was 

 discovered that more antitoxin was needed to neutralize the mixture than 

 was originally calculated, because the toxoids took no part in testing the 

 toxin, but were active in uniting with antitoxin, and in this manner 

 leaving true toxin unneutralized, and therefore toxic, unless an excess of 

 antitoxin was used. 



Analogous conditions may be observed among colloidal solutions. 

 Thus, Danysz has shown that more toxin is neutralized if antitoxin is 

 added at once than when it is added in successive doses. As stated 

 elsewhere, this is explained by Ehrlich upon the assumption that time 

 is allowed for the degeneration of toxin into toxoids to take place, the 

 latter having a greater affinity for the antitoxin. It has been shown, 

 however, that in some cases the addition of a small amount of a second 

 colloid of opposite sign to a colloidal solution may render the solution 

 more stable and protect it from precipitation by an excess of the second 

 substance. Similarly, the amount of colloid necessary to precipitate 

 a constant amount of another colloid is reduced to a minimum if the 

 addition is made at once, and is rendered much greater if the colloid 

 added is made slowly in small amounts, an interval being allowed to 

 elapse after each addition. This is closely analogous to the Danysz 

 reaction, and explains the latter as being due, when antitoxin is added 

 slowly to toxin, to the formation of transitional compounds of toxin 

 and antitoxin of diverse nature, requiring more antitoxin for complete 

 neutralization of the toxin than if the antitoxin were added at once and 

 in one dose. 



