32 
the relation of boracic arid and ammonia. These two substances have 
a comparatively Aveak 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 brought together in watery 
solution some of the ammonia at once unites with some of the boracic 
acid and forms ammonium borate. This reaction starts Avith a certain 
velocity, but as the mass of ammonium borate increases, the A^elocity 
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 alloAved to 
proceed under the giA^en conditions. 
Affien 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 
Avhether or not ammonium borate is present. But as the proportionate 
amount of ammonium borate remains constant, it is understood that 
AAffiile this continuous association between 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 ammonia and 
boracic acid These two reactions take place simultaneously. 
Arrhenius believes that the diphtheria poison changes sloAvly, accord- 
ing to the laAvs of monomolecular reactions, into a nonpoisonous body — 
toxoid. Both substances, toxin and toxoid, according to Arrhenius, 
combine feebly Avith antitoxin, the equilibrium constant being equal 
for both. 
Ehrlich, however, contends on the other hand that the diphtheria 
poison is not onl}^ a complex substance, but that the toxin and antitoxin 
have strong affinities for each other. He admits that the long inteiwal 
between the values of L” and L+ seems to oppose the acceptance of a 
strong affinity between the toxin and antitoxin. 
Designate by D the amount of toxine representing the difference 
between L+ and H. From chemical examples it can be easily shown 
that with poisons of strong avidity the value of D must correspond 
exactl}" to one minimal lethal dose, whereas with poisons of Aveak 
affinity D may be much larger on account of the free or dissociated 
poison. Ehrlich, however, finally succeeded in finding a toxine in 
which D was precisely of the theoretic value of 1. Thereb}^ it was in 
principle shown that toxin and antitoxin unite with strong affinity, 
and the great variation, from 0 to 300 per cent, in the A^alue of D rep- 
resented bA" different speciinens of toxines could be explained by the 
presence of toxone. 
