INOCULATION FOR PLEURO-PNEUMONIA IN CATTLE. 469 
to belong to the fluid, and therefore we are content to remain 
among those who do not advocate the system. As a product 
of a specific disease , conveyed from animal to animal of the same 
species , it should produce that disease , upon the principle that 
“ like begets like.” 
It is a property of an animal virus, and common to them 
all, to multiply to an unascertainable extent within the cir- 
culating fluids or blood, when introduced into the organism 
by inoculation, and subsequently to centre in some especial 
part of the body. Usually this part is either directly ex- 
ternal, or it has a free communication with the outlets of the 
body, apparently for the discharge of the morbific matter 
from the system. We observe these things especially to 
belong to the virus of smallpox, which is, however, but a type 
of the class . 
The skin in smallpox becomes the focus of the disease 
.after the multiplication of the poison has been effected. Every 
vesicle placed on the skin contains the virus ; it therefore 
partakes of the same nature, and is capable in the same man- 
ner of further extension as was the original vesicle. The 
inoculated disease is thus proved to be identical with the 
natural ; it is accompanied with the same symptoms, consti- 
tutional and local, and is alike capable of indefinite extension 
both by infection and contagion. How entirely opposed to 
these laws is the inoculation of cattle for the prevention of 
natural Pleuro-pneumonia. According to Dr. Willems and 
other advocates of the system, the virus, when introduced, 
affects the blood; augments within it; causes both local and 
constitutional disturbance ; is reproduced in the areolar tissue 
of the tail at considerable distance from the site of its inser- 
tion ; is capable of being transmitted from animal to animal ; 
gives immunity against an attack of Pleuro-pneumonia — thus 
far agreeing fully with the phenomena of genuine inoculation ; 
— and yet it never produces the disease, although it not unfrequently 
destroys the animal even weeks after its employment . 
The pillar on which inoculation stands is that of a disease 
being capable of transmission from one animal to another 
by the application of a special cause. Remove this, and it 
falls. The giving of immunity, or destroying the susceptibility 
to second attacks of the disease, are but as the ornaments of 
the capital, adding to its beauty and its value, but not to the 
necessity of its existence. 
Fortunately, however, for the ends of science, inoculation, 
or the operation of the special virus of a disease on the body, 
is so far beneficial, that nature, having freed herself of the 
materials existing in the organism which are capable of being 
