NOTES ON ATTENUATION OF VIRUS TO PREPARE A VACCINE. 
333 
of the experiments conducted by Prof. Graham in connection 
with the above article, on about sixty hogs, including over eighty 
carefully prepared and lengthy tables, which represent an amount 
of work that is inestimable. 
At the meeting of the Kentucky Veterinary Medical Associa¬ 
tion in February, Dr. Graham presented this paper in synopsis, 
covering experiments which had been carried on from time to 
time at the Kentucky Experiment Station on “ The Attenuation 
of Virus in the Blood of Cholera Hogs.” 
These experiments involved attenuations, at 50° C., 55 0 C., 
6o° C., for periods varying from one-half hour to one hour. In 
all, as we have said, about sixty pigs were inoculated with these 
various attenuations. These experiments were not carried into 
the field, but confined to the experiment station herds. 
The conclusions drawn from these inoculations were as fol¬ 
lows : “ The variation in susceptibility of swine is the seat of 
irregularity of results in these experiments; as experimentally 
shown, the amount necessary to protect one hog might be suffi¬ 
cient to kill its mate. Different strains of virus also vary in 
virulency. It would seem advisable to test the strains by animal 
inoculation, but this would not give a true insight into the 
strength of the vaccine in that the test hogs might not be suscepti¬ 
ble, and produce a perfect test. Such being obtained would not 
throw a light on the outcome of its general use, as the question 
of variation of susceptibility must be considered and ascertained 
in each herd, and each individual member of the herd, before 
regular results could be expected. 
Conclusion. 
“ 1. Inoculation of attenuated virus at 6o° C. for one hour 
may produce cholera. 
“ 2. Inoculation of attenuated virus at 6o° C. for one hour 
generally does not produce sufficient immunity to protect hogs. 
“ 3. Inoculation of attenuated virus at 6o° C. for one half 
hour generally produces the disease. 
