148 DISEASE IN WILD MAMMALS AND BIRDS 
lungs there is very commonly a colony lying in the ostium 
supplying the anterior, lateral and posterolateral ca\^ties. 
The lungs in birds are not free as in mammals, being 
fitted into the troughs made by the anterior ridges of the 
ribs, to the serous covering of wliicli they are lightly 
attached by delicate fibres running between the two. This 
more or less definite fixation, together with the pressure of 
the air in the sacs give the free play of the lungs a limited 
excursion. They are naturally very elastic by reason of 
a good supply of elastic fibers and large air spaces, a con- 
dition aided by their attachments to the supports of the 
diaphragm and to the insertions of the air sac walls. Not- 
mthstanding this elasticity and the great capacity of the 
organ for blood, it seems as if congestion of the lungs is 
a very serious matter, since from the foregoing re\"iew 
of anatomy, accommodation of excess blood and any con- 
solidation must be difficult. As a matter of fact the mere 
excess of blood kno^\ii as active congestion seems able to 
kill small varieties. 
Congestion of Lungs. 
Birds of flight seem to have little resistance to this con- 
dition and often it is the only diagnosis one can make at 
autopsy. The causes of this condition include exposure, 
dust, gorging (?), indigestion, enteritis and infection in 
birds while in mammals acute gastrointestinal disease 
stands out as the most prominent accompaniment. To 
what extent dust and exposure operate I do not see, 
although they are frequentl}'' mentioned as causes. The 
overfilling of the crop, esophagus and proventricle, the 
turgescence incident to gastric indigestion or the pressure 
of foreign bodies in large amount are supposed to operate 
by exerting pressure on the anterolateral air sacs with 
closure of their ostia and also by right lateral torsion of 
the heart with twisting of the very delicate pulmo- 
narv veins. 
