The Diseases and Feeding of Cattle. 
425 
jaw). Only one, Texas fever, is traceable to Protozoa, and one, actinomycosis, 
to a fungus. Those diseases of which the cause is unknown, or imperfectly 
worked out, are pleuro-pneumonia, rinderpest, foot-and-mouth disease, 
rabies, cowpox, malignant catarrh, and dysentery. 
The distinction between infectious diseases and contagious 
diseases is made the subject of remarks which are worth repro- 
ducing, especially as they close with the caution that to label a 
given disorder as infectious, or contagious, is a very different 
matter from really understanding the nature of the particular 
disease in question. 
Much discussion has taken place of late years concerning the precise 
meaning of the words “ infection ” and “ contagion.” But these words are now 
wholly inadequate to express the complete processes of infection, and it may 
be said that each species of Bacterium or Protozoon has its own peculiar 
way of invading the animal body, differing more or less from all the rest. 
There are, however, a few broad distinctions which may be expressed with 
the help of these old terms. Infection, as laid down above, refers at present 
in a comprehensive way to all micro-organisms capable of setting up 
disease in the body. Some micro-organisms are transmitted directly 
from one animal to another, and the diseases produced may be called “ con- 
tagious.” Among these are included pleuro-pneumonia, rinderpest, foot- 
and-mouth disease, rabies, cowpox, aud tuberculosis. Again, certain 
organisms are perhaps never transmitted from one animal to another, but 
may come from the soil. Among these are tetanus, black quarter, anthrax 
to a large extent, aud perhaps actinomycosis in part. These diseases, 
according to some authorities, may be called miasmatic. There is a third 
class of infectious diseases of which the specific bacteria are transmitted 
from one animal to another, as with the contagious diseases, but the bacteria 
may, under certain favourable conditions, find enough food iu the soil and the 
surroundings of animals to multiply to some extent after they have left the 
sick before they gain entrance into a healthy animal. 
This general classification is subject to change if we take into considera- 
tion other characteristics. Thus tuberculosis would not by many be 
considered contagious in the sense that foot-and-mouth disease is, because 
of the insidious beginning and slow course of the disease. Yet the Bacillus 
must come from pre-existing disease in either case. The disease of rabies 
or hydrophobia is not contagious in the sense that rinderpest is, because 
the virus of rabies must be inoculated into a wound before it can take 
effect. Yet in both cases the virus passes without modification from one 
animal to another, though in different ways. 
Again, all the diseases under the second group, which seem to come 
from the soil and from pastures, are in one sense contagious, in that the virus 
may be taken from a sick animal and inoculated directly into a healthy 
animal with positive result. Other illustrations may be cited which show 
that these old terms are not in themselves satisfactory. There are so many 
conditions which enter into the process of infection that no single classifi- 
cation will give a sufficiently correct or comprehensive idea of it. These 
statements will be easily understood if the different infectious diseases in the 
following pages be studied with reference to the way or ways in which each 
disease may be contracted. Enough has been said, therefore, to show that 
if we wish to make ourselves acquainted with the dangers of any given 
disease we must study that disease aud not rely upon any single word to tell 
the whole story. 
VOL. jv.’t.s. — 14 F f 
