31 
dose takes away just one -half MLD until 100 such combining units, or 
one-half of the immunity unit, has been added. A further addition 
of antitoxin had no effect upon the toxin as shown by death or necroses, 
but only inffuenced the toxone. 
In B (tig. 2). instead of an equal mixture of toxin and toxoid, known 
as hernitoxin. we have a mixture of toxin and toxoid, containing more 
of the latter than the former, as indicated by :he diminished toxicitv. 
The evidence of tritotoxAn is shown in the spectra between SO and 100. 
Phase D (tig. 2) shows a further loss of toxicity of this poison Xo. 
5 under consideration. By this time the minimal lethal dose had risen 
to 0.001. It will be seen that the addition of forty two-hundredths of 
the immunity unit had no inffuence upon the toxicity of the poison, 
indicating the appearance of prototoxoid. 
Three distinct zones may be distinguished in such spectra. 
The first zone, which is not always present, represents the non- 
poisonous prototoxoid. 
The second zone contains the poisonous toxin. 
If the addition of of the immunity unit, which represents one 
combining unit, removes exactly 1 iNILD, the poison then contains 
pure toxm. Sometimes the addition of one combining unit removes 
on the average one-half the lethal dose.* This phenomenon is inter- 
preted as indicating the mixture of equal parts of toxins and toxoids^ 
designated bv Ehrlich as hernitoxin. The existence of hemitoxin is 
possible only in case the toxoid has precisely the same avidity for the 
antitoxin as the toxin. From this it follows, as Ehrlich had from the 
beginning assumed and as Arrhenius has confirmed, that in the trans- 
formation of toxin into toxoid no change in avidity occurs. 
Pure toxoid occurs often in the form of a pjrototo:roid . which possesses 
a stronger affinity for antitoxin than all other components of the poison. 
The prototoxoid manifests its presence by the fact that a certain quan- 
tity of antitoxin may be added to the diphtheria poison without in the 
slightest degree lessening its toxicitv. 
The third zone, which Ehrlich calls the *Aoxone zone, has been 
subject to the greatest amount of discussion and the correctness of 
his views has been questioned, especially by Arrhenius and Madsen.® 
Arrhenius insists that instead of considering the diphtheria poison to 
contain toxin and toxonx. it would be simpler to consider it as a single 
(homogeneous) substance which has a very weak affinity for the anti- 
toxin. and that in mixtures containing toxine and antitoxin there is 
alwavs both free toxine and free antitoxin. He draws his analogv from 
known facts in physical chemistry, particularly from studies upon 
«Toxines et antitoxiues le poison diphterique. Acad. roy. sci. et let. Danemark: 
Bull. no. 4, 1904. pp. 269-305. 
