BIOLOGICAL PRODUCTS. 
285 
diphtheria conferred an immunity against a subsequent attack, 
it was considered that the introduction of the toxine into the 
body of an animal in non-fatal doses would cause the forma¬ 
tion of a neutralizing substance or anti-toxine and that this in 
•turn would be capable of destroying the poisonous effect of the 
toxine. This theory was sound and Von Behring prepared an 
anti-toxic serum from dogs and sheep. Aronsohn used goats 
and later Roux employed horses. While the use of the smaller 
animals established the general principle of the formation of an 
anti-toxic substance in the blood of a treated animal, the expense 
involved in the preparation of this serum would almost prohibit 
its general application if necessity required the use of the smaller 
animals. We may, therefore, consider that while Von Behring 
was the originator of the method we must credit Roux, a pupil 
of Pasteur, with the practical solution of the means by which an 
adequate amount of serum could be secured to meet the demands 
for controlling diphtheria in the human. 
Anti-bacterial and anti-toxic sera are prepared by inducing 
a high degree of immunity in the larger animals against the 
disease for which the anti-bacterial or anti-toxic sera are desired. 
The horse being a very tractable animal has proven the most 
satisfactory and is the one most frequently used. The 'horse was 
selected as a large amount of serum is available once the immuni¬ 
zing process has reached a satisfactory point. Great care, how¬ 
ever, must be exercised in the selection and subsequent care of 
the animals required for experiment. Even with the most pains¬ 
taking care one is not sure of securing a subject, the serum from 
which after the requisite treatment will show a satisfactory de¬ 
gree of potency. In some instances as many as an average of 
six horses are required to obtain one giving a satisfactory serum. 
When horses are immunized in the preparation of anti-plague 
serum, even a greater number may be required. 
The anti-bacterial and anti-toxic sera are now well and favor¬ 
ably known, having demonstrated their efficiency in preventing 
and controlling losses from the diseases for which they are pre¬ 
pared. 
