VACCINIA. (COW-POX.)
The important discovery of vaccination is due to Dr. Jenner, who ascertained that when the cow was affected by this disease and it was then communicated to man, the affection was rendered very mild and devoid of danger, and at the same time it proved a very complete protection against small-pox. Like most other valuable discoveries introduced to the world, it encountered bitter prejudice and the most unfair opposition. Now its inestimable value is generally known and admitted.
In a few cases, in which the quality of the vaccine virus was deteriorated, its effect is only to slightly-modify small-pox, and then the disease resembles that caused by inoculation. The operation of infecting the blood with the kine virus is called vaccination. All that we know is that when the cow becomes affected with this disease, and it is then transferred to man, it loses its severity and serves as a protection against small-pox. In a great majority of cases this protection is absolute, and only in a very few does it leave the subject susceptible to small-pox, materially modified. The protection it affords against small-pox is found to diminish after the lapse of an indefinite number of years, and hence it is important to be re-vaccinated once or twice, for instance, after an interval of five years. Between the second and third months of infancy is the best period for vaccination, and the place usually selected is the middle of the arm above the elbow-joint.