HOG CHOLERA 429 
first, in infected herds; second, where it cannot be used by experienced men; third, 
where the entire herd cannot receive serum, that is, no susceptible animal in a herd 
should remain untreated when any of the animals receive simultaneous treatment; 
fourth, in animals with subnormal resistance due to radical changes of feed and quar- 
ters, shipping, weaning, castrating, insanitary surroundings, etc.; fifth, in pregnant 
sows, especially those near farrowing time; sixth, in sows that are suckling pigs; 
seventh, in unweaned pigs and those weighing less than 40 pounds; eighth, in herds 
that cannot be properly isolated during the four or five weeks subsequent to treatment. 
Double treatment is indicated in cases where permanent immunity is desired with 
the least possible risk, and where its additional expense seems justified (pure-bred herds). 
It can also be used with great advantage where sows and suckling pigs are in imminent 
danger of exposure to cholera. The first dose (serum alone) protects until weaning 
time is over, and until the pigs are large enough and the sows are in proper physical 
condition to receive the second dose (simultaneous treatment). Some authorities 
question whether the passive immunity produced by the first treatment does not in 
some cases completely inactivate the virus given in the second treatment, so that 
sometimes only a temporary immunity follows the double treatment. While accumu- 
lating evidence indicates that the ultimate effects of double treatment and simultaneous 
treatment are identical, it is nevertheless prudent to prolong the time between treat- 
ments to a reasonable limit (3 to 6 weeks) of safety. 
Usual method of serum preparation. A hog is immunized with a dose of virus, usually 
2 ce., and sufficient serum to protect. After the resulting reaction is over (in 10-14 
days) the animal is hyperimmunized by an intravenous injection of virus—65 cc. for 
each pound of weight. (The virus used is defibrinated, and preferably cooled, blood 
from pigs killed while in the height of an attack of acute hog-cholera. The pigs are 
infected with intramuscular injections of small doses of virus. The essential require- 
ments are that the pigs shall show marked symptoms of acute hog cholera, that they 
shall be ready to kill in 7-14 days from the date of injection, that they shall show 
pronounced lesions of acute hog cholera, and no evidence of other infectious diseases). 
In about two weeks after the serum hog is hyperimmunized it is bled from the tail. 
Subsequently it is bled each week until the bleedings of a series number three or four. 
Then the immunity is reinforced by a second injection of virus—usually one-half the 
original amount. This is followed in about ten days by the first bleeding of a second 
series. Sometimes there is a third or even a fourth dose of virus each followed by three 
or four weekly bleedings. The final bleeding takes place from the throat. Each time 
blood is drawn it is immediately defibrinated, cooled, and preserved by the addition 
of one part in ten of 5% phenol. It is then stored in a dark cool place until enough is 
on hand for a test. 
When a test is to be made the serum is poured into a large container, mixed thor- 
oughly, a sample is drawn for testing, and the remainder is placed in bottles for shipping. 
The bottles are sealed and refrigerated. Eight pigs, preferably of the same litter and 
weighing 50-75 pounds each, are chosen for the test. Each receives 2 cc. of virus. 
Two receive 15 cc. each of serum, two receive 20 cc. each of serum, two receive 25 cc. 
each of serum, and the remaining two receive no serum. The pigs are marked for 
identification, placed together and given like care. Daily temperatures are taken. 
The requirements are that the pigs receiving virus alone shall sicken and reach a dying 
condition in 7-14 days from the date of injection, and display on post-mortem marked 
lesions of acute hog cholera; also that the pigs that receive virus and serum shall recover 
