32 
the relation of boracic acid and ammonia. These two substances have 
a comparatively weak affinity for each other, and in mixtures all the 
boracic acid does not combine with the ammonia, but there is always 
present both free ammonia and free boracic acid. 
When ammonia and boracic acid are broug’ht together in watery 
solution some of the ammonia at once unites with some of the boracic 
acid and forms ammonium borate. This reaction starts with a certain 
velocity, but as the mass of ammonium borate increases, the velocity 
of the reaction gradually diminishes. After a time a condition is 
reached when the ammonium borate has a maximum value and does 
not further increase, no matter how long the reaction is allowed to 
proceed under the given conditions. 
When this condition of equilibrium is reached the mass contains a 
constant quantity of water, ammonia, boracic acid, and ammonium 
borate; but these substances are not at rest. The ammonia and 
boracic acid will always react when in the presence of each other 
whether or not ammonium borate is present. But as the proportionate 
amount of ammonium borate remains constant, it is understood that 
while this continuous association lietween the ammonia and the boracic 
acid is going on there is, at the same time, a reversible action — that is, 
a dissociation of the ammonium borate to re-form aimnonia and 
boracic acid These two reactions take place simultaneously. 
Arrhenius believes that the diphtheria poison changes slowly, accord- 
ing to the laws of monomolecular reactions, into a nonpoisonous body — 
toxoid. Both substances, toxin and toxoid, according to Arrhenius, 
combine feebly with antitoxin, the equilibrium constant being equal 
for both. 
Ehrlich, however, contends on the other hand that the diphtheria 
poison is not onh" a complex substance, lint that the to.vin and antitoxin 
have strong affinities for each other. He admits that the long interval 
between the values of L® and L-h seems to oppose the acceptance of a 
strong affinity between the toxin and antitoxin. 
Designate b}" D the amount of toxine representing the dilference 
between L-(- and L®. From chemical examples it can be easily shown 
that with poisons of strong avidity the value of D must correspond 
exactly to one minimal lethal dose, whereas with poisons of weak 
affinitv D may be much larger on account of the free or dissociated 
poison. Ehrlich, however, linalH succeeded in hnding a toxine in 
which D was precisely of the theoretic value of 1. Thereby it was in 
principle shown that toxin and antitoxin unite with strong affinitv, 
and the great variation, from 0 to 300 per cent, in the value of D rep- 
resented by dilferent specimens of toxines could be explained by the 
presence of toxone. 
