510 
HENRY STEWART. 
that so far as these virulent diseases are eoucerued, it is certain, 
and unavoidable, that their germs are widely distributed, as are 
those of the common moulds and mildews, the rusts and smuts of 
vegetation and the virus of cholera-morbus, yellow fever, typhoid 
fevers, small-pox and other contagious diseases of man ; and 
chicken cholera, swine cholera, pleuro-pneumonia and anthrax 
fevers of cattle. We cannot doubt this to be a fact unless we 
can show that there is a special law by which these diseases of cat¬ 
tle are differentiated from similar diseases of mankind and plants. 
For we can show by numberless instances how infectious diseases 
occur in mankind through favoring causes for the development of 
germs already in existence and without any exposure to infection, 
and how a large number of persons in the closest contact possible 
with the virus escape the infection. Indeed, the fundamental 
theory of vaccination or inoculation is based upon this very fact 
that the blood may be brought into such a condition that the 
germs of the special disease cannot grow in it, however much 
it may be exposed to, and infected by them. Again, the precau¬ 
tions by which physicians fortify themselves against infection 
would always be useless and ineffective if it were not possible by 
such precautions to give the blood the power of rendering the in¬ 
haled infection harmless, while on the contrary it is the person 
who is exhausted, enervated by care and worry, or debilitated by 
any cause who becomes the early victim. Thus Prof. Law, than 
whom we have no higher authority in this respect, says of anthrax 
fever, that “ its development (!) is determined (among other causes) 
by a condition of the system of the animal predisposing to the 
reception and growth of the poison * * * by overwork, impure 
air and unsuitable food or water, * * * sudden chills when the 
poison is present, as extreme variations in the temperature * * * 
and a still, close atmosphere.” 
In conclusion I would urge the following facts, viz.: that the 
contagion of this class of diseases, including pleuro-pneumonia, 
must necessarily be widely spread abroad ; that the virus is able 
to exist under favorable circumstances for a long time ; that it 
may and does remain dormant in the blood of animals, waiting 
for a train of circumstances favoring its development; and that 
