SECTION XVII— PART 4 
ACUTE DISEASES RESEMBLING THE SPECIFIC 
INFECTIONS OF DOMESTIC ANIMALS 
Specific communicable diseases are sometimes divided 
into those most often encountered as ''herd diseases" and 
those which appear as single cases or in small groups. 
This would seem to imply that the first behave as easily 
disseminated epizootics, their virus passing from animal 
to animal simply by proximity or by casual contact where- 
as the transfer of infective material is less readily ac- 
complished by the second group, often demanding special 
assistance. Foot-and-mouth disease, pleural pneumonia, 
cattle plague, and influenza illustrate the epizootics while 
tetanus, rabies, quarter-ill, malignant edema, and infec- 
tious vaginitis are examples of less easily transferred 
processes. 
It is not intended that these remarks shall cover all 
possible means of transmission but instead they are in- 
tended to focus attention upon the sources of viruses 
whereby animals become infected. An original case must 
always be present in order for spread to occur. Where 
animals are being added to a herd a new comer may be 
diseased or the carrier of a virus; when animals are 
transported for sale or other reason, infection may be 
met in a new stall, conveyance or pasture ; contaminated 
food may be offered. In menageries, with specimens, 
single or in small groups, and arrivals always quarantined 
before other animals are exposed, acute specific infections 
seldom appear. It is also improbable that a wild animal, 
infected at its source or in some dealer's place, would 
survive the journey and arrive in an infective condition. 
Consultation with the reports of other gardens fails 
to discover records of any serious outbreaks of epizootic 
disease except for fowl cholera and distemper, examples 
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