T. S. BILLINGS. 
247 
has been passed through a succession of animal generations— 
retro-vaccine—or the primary variola vaccine—vaccinated variola 
—won by the inoculation of variola from man to cattle ? Th e 
so-called animal vaccine—cultivated vaccine—is in my opinion 
nothing more than retro-vaccine originally derived from human¬ 
ized vaccine, which derives its present cognomen of a animal ” 
on account of its being passed through several generations of 
calves, and forms a sort of u potentized retro vaccine.” In proof 
of the same, T will say, that inoculations of human beings with such 
long cultivated animal vaccine give in general the same favorable 
results, as inoculation with retro-vaccine which has been directly 
won from humanized lymph. We have yet to make a few 
remarks over certain properties of the contagium of variola 
vaccina , which have a general pathological interest. 
As is known, the contagious elements of vaccine are always 
of a fixed nature. If our views are correct over the origin of 
variola vaccina, vaccine offers an example of a metamorphosis 
taking place in the bovine organisms by means of which the 
original volatile contagium of variola is transformed into the 
fixed vaccine. If we assume, which at the present day is scarcely 
doubted, that the aetiological and to all intents identical conta¬ 
gium of both human and bovine variola is of a corpuscular 
nature, it is in all cases difficult to understand why the same con¬ 
tagium is at one time in condition to penetrate the human organ¬ 
ism by means of the atmosphere, and why it is only dangerous to 
the bovine organism in a fixed condition; especially is this the 
case when we remember that vaccine is easily conserved in a des- 
sicated form and possesses an important degree of tenacity, which 
it soon loses in a fluid form. Fluid vaccine lymph generally 
loses its activity in from five to eight days; it is not definitely 
known whether it is in consequence of peculiar processes of decom¬ 
position, or from physical conditions—coagulation of the lymph. 
Basing ourselves upon numerous experiments which we shall pre¬ 
sently consider, we may assume that vaccine contagium is only in 
condition to produce its specific pustule and to reproduce itself 
when it comes in contact with a wounded part of the corium, 
while, according to experience, it remains inactive from the lungs, 
