DIPHTHERIA BACILLUS. 363 
the antitoxin strength increases. It seems, therefore, 
from the above facts that diphtheria antitoxin has the 
characteristics of the globulins. Whether it is a union 
of diphtheria toxin and globulin, or an increase of cer- 
tain globulin-like substances through the stimulation of 
the toxin, we have as yet no facts to tell us. Antitoxin 
is destroyed by prolonged moderate heat (60° C.) and 
by short exposure to higher temperatures (95° to 100° 
C.). It is much less sensitive than diphtheria toxin. 
Diphtheria antitoxin has the power of neutralizing 
diphtheria toxin, so that when a certain amount is in- 
jected into an animal before or together with the toxin 
it overcomes its poisonous action. As already stated, 
there is a great difference of opinion as to whether anti- 
toxin acts by direct chemical neutralization of the toxin 
or indirectly on the cells. The facts in favor of a direct 
action of antitoxins upon their corresponding toxins 
have recently been briefly summarized by Cobbett as 
follows : 
1. Certain reactions have been observed to take 
place between these substances outside the animal body 
(venom, ric‘n, crotin, tetanus toxin, diphtheria toxin, 
and their corresponding antitoxins). 
2. Various attempts to separate the toxins and anti- 
toxins from neutral mixtures have been failures. Par- 
tial successes have, at least in some instances, been 
shown to depend upon the fact that insufficient time for 
their complete union was allowed, separation being no 
longer possible if this were granted. 
3. The accuracy of the titration of toxins and anti- 
toxins to within 1 per cent. of error. 
4. The fact that to save an animal from 1000 fatal 
doses of diphtheria toxin requires little more than a 
