These facts explain why it has always been so difficult to preserve and cultivate vaccine in tropical regions.
Mixed with equal parts of neutral glycerine, the virulent material preserves its activity unimpaired for from six to eight months.
The disease develops equally in man, the horse, the ox, the buffalo, the goat, and the camel. Its development is less typical in the pig, sheep, dog, and rabbit. Young animals are best adapted for its cultivation.
The blood and serum of animals suffering from cow-pox possess immunising properties, but only when administered in very large doses, say from 6 to 12 lbs. of blood, or ½ to 1 lb. of serum.
The curative action of this serum against small-pox is comparatively trifling.
The diagnosis of cow-pox is not very difficult.
At first the disease might be mistaken for false cow-pox, the eruptions of foot-and-mouth disease, or gangrenous coryza.
In false cow-pox, the nature of which is also little understood, although it is known to be contagious and is regarded by some as true vaccinia, the pustules are smaller and thinner, while the vesicle is more developed, and the disease runs a more rapid course.
In foot-and-mouth disease the eruptions are of the nature of vesicles or bullæ, not pustules. The eruption occurs in twenty-four hours or less, and can only be mistaken for vaccinia during the period of desiccation and the formation of crusts.
Finally, as regards gangrenous coryza, the hardened pustules do not produce vesicles.