140 Annual Report for 1905 of Royal Veterinary College. 
experiments, the earliest and most important of which were 
carried out in Germany at the instance of Yon Behring. 
The chief impetus to these experiments was the discovery 
that the bacilli which are the cause of tuberculosis in man 
and various species of the lower animals have very different 
degrees of virulence, and especially the discovery that the 
bacilli which are present in the majority of cases of human 
tuberculosis have only feeble powers for exciting disease in 
cattle. This latter fact, of course, suggested that among 
these weaker strains or varieties of tubercle bacilli there 
might be found some which could safely be used as “ vaccine,” 
that is to say, might be injected into cattle with the object 
of setting up a mild non-dangerous attack of tuberculosis, 
terminating in complete recovery, and leaving the animal so 
treated with a serviceable degree of immunity. Such a process 
would be strictly analogous to the vaccination of human beings 
against small-pox, for there is reason to believe that the disease 
which is known as cow-pox is caused by a feebly virulent 
variety of the organism which is responsible for human 
small-pox. 
The experiments referred to above have during the last 
two years been followed with interest by all who were 
acquainted with them, and, as it may now safely be said that 
they have passed beyond the laboratory stage, it appears to be 
desirable to call the attention of British stock owners to the 
enormously important prospect which they open up. Briefly 
it may be said that they appear to justify the assertion that we 
have now at our command a comparatively safe and inexpen- 
sive method of vaccinating cattle against tuberculosis. 
The first point in connection with the method is to select 
from the various available strains of tubercle bacilli one which 
has been proved by preliminary experiments to be of very low 
virulence for cattle. This is not a matter of any real difficulty, 
for the majority of the strains which are found in human 
lesions appear to be incapable, in small doses, of killing cattle 
with tuberculosis, or of setting up more than a temporary 
disease. Experiments also indicate that the bacilli which are 
found in the lesions of tuberculosis of fowls may be used for 
the purpose. 
Having obtained a suitable strain of tubercle bacilli, these 
are grown in artificial cultures in the laboratory, and employed 
as the vaccin, which is injected in definite dose into one of the 
jugular veins of the animal to be vaccinated. It is not yet 
possible to say whether a sufficient degree of immunity can 
be conferred by a single injection of a dose which involves 
no risk to the animal, or whether it may be found better to 
vaccinate the animal twice, viz., first with a very feeble vaccin, 
