50 THE PRINCIPLES OF IMMUNOLOGY 



heat and could by heat be dissociated from the thermolabile anti- 

 lysin. The subsequent chemical neutralization of the toxin (or 

 lysin) resulted in the restoration of its toxicity. In this laboratory 

 Wahl has shown that titration of diphtheria toxin using normal 

 guinea-pigs in one series and guinea-pigs with only one kidney in 

 another, gives materially different results. These experiments were 

 carefully controlled and may be offered as a further indication of the 

 loose combination and its corollary the reversibility of the reaction, 

 on the probable assumption that the toxin is more readily excreted 

 by the animals with two kidneys than by those with one. The 

 recitation of these few experiments to which others might be added 

 is sufficient to illustrate the objection to the Ehrlich theory of fixed 

 combination, and two other important hypotheses are offered for 

 consideration : (i) The conception that the combination follows the 

 law of mass action and (2) the theory of colloidal reaction. 



The Law of Mass Action. The application of the law of mass 

 action has been worked on by Arrhenius and Madsen principally. 

 This law is usually illustrated in the chemical laboratories by the 

 reaction between one gram molecule ethyl alcohol and one gram 

 molecule acetic acid which yields ethyl acetate and water, the reac- 

 tion, however, stopping at a point of equilibrium where there is 

 found in the mixture ^3 gram molecule alcohol, l /$ gram molecule 

 acetic acid, 2 /z gram molecule ethyl acetate, and 2 /z gram molecule 

 water. The same end-result is obtained if instead of mixing ethyl 

 alcohol and acetic acid, we mix ethyl acetate and water, thus indicat- 

 ing the reversibility of the reaction as stated in the formula : 



C,H 6 OH + CH 3 COOH ^ CH 8 COOC 2 H 5 + H 2 O 



Arrhenius and Madsen compared the reaction between tetanoly- 

 sin and its antitoxin and the reaction between boric acid and am- 

 monia. This was of advantage because ammonia is hemolytic and 

 boric acid is not. Thus a reversible reaction is found in which the 

 addition of boric acid reduces the hemolytic activity of the ammonia. 

 As with the alcohol-acetic acid experiment, however, a point of 

 equilibrium is established whereby there .always remains a small 

 amount of free ammonia in spite of the addition of boric acid to a 

 point of saturation. The same general proposition holds in regard 

 to tetanolysin and antilysin, and these authors were able to con- 

 struct similar curves of neutralization for both of these reactions. 

 With this idea as a basis, the late paralyses of diphtheria, either ex- 

 perimental or clinical, would depend not upon the toxon of Ehrlich, 

 but rather upon a small non-fatal amount of toxin that is never com- 

 pletely neutralized in the reaction. 



The Danysz Effect. It will readily be seen, however, that the 

 reversible reactions illustrating the law of mass action deal with 

 crystalloids, while it is probable both toxins and antitoxins are of 

 colloidal character. Certain colloids are known as " reversible col- 



