176 TUBERCULOSIS IN SWINE 
Koch pointed out that it was necessary to produce a bacterial as well 
as a toxic immunity. Tubercle bacteria of all varieties have been 
tried. Von Behring thought he had succeeded with his ‘‘bovo- 
vaccine”’ but its use was not satisfactory. Pearson and Gilliland did 
much work on this subject but a practical method for immunizing 
cattle has not been formulated although experimentally a certain 
amount of resistance can be produced. 
The conclusions drawn from the recently reported extended investi- 
gations of M’Fadyean, Sheather, Edwards and Minett in the produc- 
tion of immunity against tuberculosis in cattle with the avian and 
human varieties of the organism are as follows: 
“By the intravenous inoculation of avian tubercle bacilli it is 
possible to confer on healthy calves a markedly increased power of 
resistance to infection with bacilli of the bovine type. 
“Such a method of vaccinating young cattle against tuberculosis 
involves little or no risk to the animals. 
“When the vaccination of young cattle against tuberculosis is con- 
sidered advisable avian bacilli should be preferred to human, in order 
to avoid the danger of infecting human beings with bacilli persisting 
in the bodies of the vaccinated animals and passed out with their 
milk.” 
Specific biological treatment. There is as yet no method of success- 
fully treating tuberculosis by any serum or bacterin. Certain physi- 
cians report good results from the use of tuberculin in selected cases. 
This does not hold for cattle although a good many infected animals 
that reacted to tuberculin seem to have had the disease arrested or to 
have recovered and thereafter fail to react. 
TUBERCULOSIS IN SWINE 
Channels of infection. In most cases infection takes place by inges- 
tion. The pig easily becomes tuberculous when fed on material rich 
in tubercle bacteria. Many illustrations of this are found in pigs 
fed on the refuse from dairies and cheese manufactories in districts 
where there is much tuberculosis in cattle or on tuberculous viscera in 
slaughter houses. Mohler found that when hogs were fed on tubercu- 
lous milk for three days, and killed and examined 107 days later 
83.3 per cent. were tuberculous. Hogs that received infected milk 
for 30 days and were allowed to live fifty days thereafter were all 
