32 PATHOGENESIS 
affected from the normal habitat in the upper air passages as on the 
hypothesis of a specific infection. It is in these instances that we 
are seeking for the crucial test for specific streptococcic etiology. 
In cases of infection resulting in bacteriemia, or in those where the 
disease is more localized, as in strangles or mastitis, and possibly in 
others where the affection spreads more or less rapidly as in erysipelas, 
we cannot well escape from the feeling that the streptococci, present 
in such large numbers, must either stand in a causal relation to the 
disease or be accounted for by their rapid proliferation in the tissues 
in association with the true etiological factor. Their natural distribu- 
tion is so wide and their virulence so capricious that a secondary 
invasion, which seems always to be possible, renders the fixing of 
etiological responsibility upon a streptococcus isolated from any 
diseased tissue a somewhat difficult task. The problems in this con- 
nection which concern us most and which need more extended investi- 
gation pertain (1) to the determination of the pathogenic possibilities 
of streptococci existing in their natural habitat and (2) to the dis- 
tinction, if it exists, between streptococci that are able to produce 
local inflammatory processes leading to suppuration and those which 
produce specific diseases, such as erysipelas and strangles. 
Pathogenesis. The pyogenic streptococci (Strep. pyogenes and 
its varieties) are the most important pathogenic species for animals 
in this genus. It has been found to be impossible to differentiate 
this species from several streptococci that have been considered the 
cause of certain diseases such as strangles in horses and erysipelas 
in cattle. In the absence of verified results to prove the non-specific 
relation of these streptococci to the diseases which have with reason- 
able certainty been attributed to this genus of bacteria, they are 
included among the specific streptococci maladies. It is very 
important, especially when the use of antistreptococcic serums are 
im question, to take into account the apparently large number of 
forms, or species, commonly included in the general statement of a 
streptococcus infection. In 1897, Van de Velde, in a very exhaustive 
series of experiments, showed that an antitoxin produced from one 
streptococcus will not immunize against another, save to a very 
slight degree. Better results are reported by the use of polyvalent 
serums. 
There are a number of acute disorders, such as vaginitis in cows, 
that have been attributed to this genus. 
