EDITORIAL OBSERVATIONS. 
847 
animals attacked soon recover, while at other times its 
spreading is rapid, and its victims suffer severely from its 
invasion. 
Occasionally it has happened, as in the experiments at 
the Brown Institution a few years ago, that animals have 
been infected with great difficulty and only after repeated 
attempts, although large quantities of virus were employed ; 
at other times, as recently at the Foreign Cattle Market at 
Deptford, the landing of a single cargo of animals, among 
which the disease appeared, the virus appears to cling to 
persons and substances so tenaciously that the disease con¬ 
tinues to break out, notwithstanding all the precautions 
which were taken to prevent it. 
Both in man and in the lower animals it is certainly the 
case that the spreading of an infectious disease depends more 
upon the degree of receptivity in individuals who are ex¬ 
posed to its influence than upon the presence or even the 
quantity of the infective matter. 
Considerable importance must be attached to the circum¬ 
stances, to which reference has been made, both from a 
pathological and sanitary point of view. It must, in fine, 
be evident that when a disease manifests a tendency to 
extend its area by mediate contagion the receptivity of sus¬ 
ceptible animals must be unusually great, and, therefore, 
that all available sanitary measures have need to be imposed 
with more than common severity. Ordinary regulations 
which affect merely the movements of diseased animals are, 
under the new conditions, found to be insufficient, and 
restrictions have to be insisted on in regard to individuals not 
susceptible to the disease; and substances which may act as 
carriers of the poison agents, it may be remarked, are all the 
more dangerous, because they are likely to escape suspicion ; 
and in dealing with outbreaks of the contagious maladies 
the sanitarian is always required to be on his guard, or his 
most elaborate precautions are rendered nugatory through 
the subtle influences of mediate contagion. 
