138 
HOUSEHOLD BACTERIOLOGY 
immunized. But these did not furnish enough. So at 
last the horse was tried, and was found admirably 
adapted to the purpose. He lends himself readily to 
the increasing doses of the potent diphtheria poison; 
he is easily rendered immune, and he furnishes without 
especial inconvenience a large quantity of blood. In 
fact, he makes no more fuss about losing blood than 
did the old people along in the early part of the last 
century, who were quite accustomed in the springtime, 
when they felt a bit heavy and had a little headache, 
to drop into the nearest barber shop to be bled. 
The preparation of diphtheria antitoxin has been 
brought to a high state of perfection. The horses 
are first very carefully tested so as to be certain that 
they have no disease. They are well fed and groomed, 
and suitably exercised. At first a small amount of the 
diphtheria toxin is injected beneath the skin. After 
a few days a larger dose is given, and then at intervals 
larger and larger quantities, until at last the horse is 
receiving such an amount in a single dose as if given 
at first would have sufficed to kill not only one but 
many horses. He has not had diphtheria at all, but 
he is now poison-proof—immune. 
■The animal is then bled from the large vein in the 
neck, the greatest care being taken, by cleansing of the 
skin, the use of sterilized instruments, etc., that no 
outside germ shall get into the blood as it flows. This 
blood is set aside in a cool place, and presently, as the 
clot forms, the serum separates in considerable quan- 
