4 INFECTION 
We cannot, therefore, dismiss the subject of infection without a 
passing consideration of the possible etiological significance, under 
certain conditions, of many species of bacteria ordinarily not clas- 
sified among the pathogenic forms but which more or less constantly 
surround the body. In the search for the cause of many lesions 
supposed from their nature to be infectious, or in applying methods 
for their prevention, it is well to take into consideration microérgan- 
isms which might possibly be the causative factors and not limit 
the search to the already recognized pathogenic species. Recent 
investigations point to the conclusion that domesticated animals 
quite frequently suffer as the result of the invasion of bacteria at 
present not listed among the pathogenic microérganisms. 
Wound Infection. Wound infections are the direct results of 
the entrance of certain microérganisms into traumatisms and opera- 
tive incisions. They fall very naturally into two classes: 
Infections producing local, acute or more chronic inflammatory 
processes usually leading to suppuration and finally healing by 
granulation. This is the form most frequently encountered clini- 
cally. The lesions are those described under acute or chronic inflam- 
mation. 
Infections which may in the beginning appear like the first or 
which may cause so little disturbance as to be unnoticed at the time, 
but later result in a local or remotely situated lesion or lesions. 
Frequently these are recognized as distinct diseases although in 
some cases, such as scirrhous cord, the origin is easily traced to an 
operation where infection was possible. 
In wound infection, the invading organism is not always of the 
same species. It is because wound infection lesions anatomically 
of a similar character may be caused by a number of different bacteria 
that they are not classed among the specific infectious diseases. 
It has been observed further, that in many lesions two or more 
species of bacteria have been associated and probably share the 
responsibility for the results. There is no symptom, or manifesta- 
tion of tissue changes, by which one can determine positively the 
exciting cause, without a bacteriological examination. 
Another class of diseases that are sometimes called wound infec- 
tions should be mentioned, namely, those specific diseases, such as 
tetanus, where the virus is introduced through a wound either in the 
skin or a mucous membrane. 
