30 S 
D. E. SALMON. 
multiples prodigiously; its vitality is so tenacious that it multiplies 
also, though but slowly, when exposed to free atmospheric air. 
In order to demonstrate that aphtous virus is truly the virulent 
agent of foot and mouth disease, numerous cultures in appropriate 
liquids have been made in Italy, but principally on a large scale 
in the laboratory of Dr. Nosotti. 
From the numerous obervations he has made, he believes him¬ 
self justified in affirming: that the microbes observed first by Prof. 
Rivolta, and better studied and for the first time cultivated by 
himself \ represent the true point of origin of the disease of epi¬ 
zootic aphta , the essence and nature of the aphtous virus. 
To confirm the virulency of his cultivation, Dr. N. has inocu¬ 
lated adult animals and has succeeded in producing with them a 
benign aphtous fever. 
After reporting a few experiments, probably too few to justify 
a thorough conclusion, Dr. N. concludes his report by declaring: 
1st. That epizootic aphta is not a disease susceptible of de¬ 
veloping itself spontaneously. It is not an indigenous, but an 
exotic disease. 
2d. Its nature is eminently contagious. 
3d. Its virulent element is represented by microbes, discovered 
first by Rivolta. 
4th. The virus can be cultivated when placed in appropriate 
media, and by successive cultures reducing its virulency, it may 
become a safe and proper agent of inoculation. 
IMMUNITY FROM CONTAGIOUS DISEASES.* 
By D. E. Salmon, D.V.M., Washington, D. C. 
Although the theory of immunity which I formulated several 
years ago has been given a prominent place in recent discussions, 
it was not my intention to take any part in this philosophizing so 
long as my views were treated with ordinary consideration and 
fairness. This theory was not developed as a mere piece of spec¬ 
ulation to while away an idle hour, nor was its object to excite 
♦From the N. 7. Medical Journal. 
