36 DISEASE IN WILD MAMMALS AND BIRDS 
clear, at least for the entities of which we have exact data, 
based upon comparisons with man and domestic animals. 
There seems to be no essential difference among 
mammals between the pathological pictures of infectious 
septicemias, the mucous and serous membrane inflam- 
mations and tuberculosis for example. They are 
characterized by fibrinous, purulent or infiltrative 
inflammations which may go on to necrosis or repair, by 
fever, by leucocytosis and by evidences of resistance — all 
of these things occurring in a similar way throughout the 
class. Of course not all animals are receptive to all 
infections since specific racial and generic immunities 
exist, but the basic response in terms of pathology is 
similar. There are no normal means of judging the sus- 
ceptibility of wild animals on their native heath to the 
important pathogens of civilization, pneumococci, strep- 
tococci, staphylococci, cholera bacilli, the typhocolon 
group, the Friedlander group and others, but it is inter- 
esting to note that in captive conditions they evince some 
receptivity to these germs or their congeners. The pneu- 
mococcus takes a fairly heavy toll in zoological collections 
every year and the Friedlander bacillus, not a very com- 
mon cause of human pneumonitis, has been seen here and 
at London. 
Among the birds, however, quite distinct differences 
in some pathological processes occur, not only from the 
mammals but also within the class. As a whole birds 
do not produce pus as we know it in man, probably 
because of the absence from their leucocytes of a 
protein-splitting ferment; their leucocyte-producing 
organs do not seem to respond as readily to a virus, 
the place of purulent exudate being taken by a coagu- 
lum or necrosis. The former varies from a clear 
gelatin-like material seen upon serous surfaces to a thick 
mat or mass of coarse but short fibrinous strands. 
Necrosis may succeed upon the latter or occur so 
promptly as to appear like the original form of 
