D. E. SALMON. 
C>8 
body of the strong virus of the malady, and it is only a ques¬ 
tion of the size of the dose whether the disease produced by 
this operation is mild or fatal in its character. 
The dose is not the only factor which influences the result 
that follows inoculation. The strength of the virus varies so 
much in different outbreaks of the same disease, that a per¬ 
fectly harmless dose obtained from one outbreak would cer¬ 
tainly be fatal when obtained from another. 
There is another influence which has an even greater effect 
in varying the results of inoculation, and that is the wide dif¬ 
ference in the susceptibility of the animals. A dose of virus 
that will scarcely affect one animal will kill another in the 
same herd, and there is also such a great difference in the sus¬ 
ceptibility in different herds that the dose which might be 
' used on one herd without producing any noticeable effects 
would set up a disease in another herd and cause the loss of a 
majority of the animals. 
With these varying conditions, which in many cases can 
neither be foreseen nor controlled, inoculation is an operation 
which is attended with more or less danger of producing the 
very disease which we are seeking to avoid. In our experi¬ 
ments we found that a dose of i cubic centimeter, i. e., from 
15 to 20 drops, of the strongest cultivated virus would occa¬ 
sionally kill an animal. From one-quarter to one-half this 
quantity, i.e., from 4 to 10 drops, have been given without 
serious consequences in any case. 
Such doses generally produce a swelling where injected, 
which is at first warm and more or less painful, and later be¬ 
comes encysted. The centre softens, disintegrates and be¬ 
comes a purulent mass, which may remain encysted or may 
force an opening through the skin and discharge for several 
weeks. An inoculation of this kind produces a slight degree 
of immunity, because a second inoculation can then be made 
with two or three cubic centimeters of virus, i. e., with four 
to twelve times the first dose, and still no fatal effects result. 
The second inoculation increases the immunity, but still 
the animals are not able to resist the effects of feeding with 
strong virus or exposure in pens where sick animals are kept. 
