Infectious Diseases of Animals. 
483 
lopment of various maladies to a considerable degree. There 
are certain affections, for example, in Eastern Europe which 
appear to spread by contagion. These affections, as they are 
represented in our country, are usually confined to the localities 
in which they appear, and never extend to a distance in the 
way that ordinary infectious and contagious diseases are known 
to do. 
Various forms of blood disease which are known by the terms 
" anthrax " or " charbon " seem to be highly infectious in some 
parts of the continent, and instances have occurred, even in Ire- 
land, of the spread of these maladies apparently from infection. 
But in England this peculiarity has not been observed. These 
diseases very commonly occur under certain conditions of soil 
and management of animals, but they never extend beyond the 
district and seldom beyond the premises in which they arise. 
Contagious and infectious diseases are presumed to be com- 
municated by means of certain " germs " in which the con- 
tagious property resides. The term " contagium " has been 
suggested by Dr. Beale as a convenient one for the purpose of 
expressing this quality. 
Sometimes it is necessary for actual contact to take place 
either between the healthy and diseased animal, or between the 
healthy animal and some of the secretions or excretions from 
the sick one. In other cases it appears that the particles of con- 
tagium are so exceedingly minute that they may be conveyed in 
the animal's breath, the exhalations from the surface generally, 
and may be wafted by the atmosphere to a considerable dis- 
tance. 
The term " volatile " which has been used to express this 
ready diff"usibility of the contagium is by no means well chosen. 
Indeed it is almost certain that the assumption of the gaseous 
form would necessitate the destruction of that vitality on which 
the activity of contagium depends. 
Considerable mystery commonly attends the progress of an 
infectious malady. An outbreak occurs in a particular part of 
a district ; a number of animals in the immediate neighbour- 
hood are affected in the ordinary course of the disease, and 
there is no difficulty in tracing the methods of communication of 
the contagium from the original centre. But suddenly the dis- 
ease appears in a new district some miles distant from the place 
where the outbreak occuri'ed, and no communication whatever 
can be shown to exist between the two localities. 
In such instances it is sometimes discovered, and it may be 
generally assumed that the " contagium " has been conveyed 
indirectly by the agency of persons or substances which have 
been in contact with the diseased animals. 
VOL. IX. — S. S. • 2 K 
