CONTRIBUTION TO THE STUDY OF SERUM-THERAPY IN DIPHTHERIA. 
665 
immunity, it is a question whether it is best to maintain this 
immunity by means of frequent subcutaneous injections of 
small amounts of toxine, or by the occasional introduction of 
larger amounts within their veins. The second process is the 
handiest, the toxine (300 to 500 cc.) is injected at the time the 
animal is bled, and he is allowed to rest for about twenty days, 
but it is less efficacious than the first. In experiments on the 
immunization of animals against tetanus, Vailliard and Roux 
found that the most active serum was obtained by multiplying 
small injections of toxine. The same is true in diphtheria. It 
would seem that the cells must be frequently excited in order to 
constantly secrete antitoxine. 
in. Anti-diphtheritic serum .—When a certain amount of 
the serum of an animal, that has been immunized against diph¬ 
theria, is added to diphtheritic toxine, the latter becomes harm¬ 
less. .The mixture, made in proper proportion and injected to 
animals, causes them no trouble and does not even determine a 
local reaction. The toxine appears to be saturated. This ac¬ 
tion not only takes place in vitro , but also occurs within the 
body. An animal protected by a sufficient dose of serum will 
not be affected by doses of toxine that would prove mortal in 
other animals. The toxine may even be injected first, and the 
serum several hours later, and the animal will not die. Of 
course the amount of serum needed to save him will vary ac- 
coiding to his weight, to the dose of toxine that has been 
given, and to the moment at which the intervention is decided 
upon. The serum is preservative and therapeutic, not only for 
the toxine, but also for the living poison. These properties, 
discovered by Behring, are the basis of the treatment, and are 
due to a special substance called antitoxine, whose nature is as 
much hidden to us as that of the toxine itself. These two sub¬ 
stances possess common characters ; they are altered by heat, 
precipitated by alcohol, and carried down by divers amorphous 
precipitates which may be produced in the liquids in which they 
are in solution. These peculiarities are common to nearly all 
the preventive or antitoxic substances which exist in the serum 
