INTRODUCTION 37 
degeneration. It is usually rapid, accompanied by a 
circumferential congestion but not associated with active 
phagocytosis. Giant ceU production is variable, but when 
developed the appearance is like that of large syncytia. 
Hemolysis is not marked in the simple infections but a 
hyperplasia of the mononuclear nodes of the liver is the 
rule. The function of this nodal increase is not quite 
clear. It has been always thought that the scanty bone 
marrow would supply the necessary erythrocytes, but we 
have seen these mononuclear areas fuU of pale red cells 
fitted with round nuclei and without pigment. The fibrin 
mentioned above does not have the delicate interweaving 
that we know in a fibrinous exudate in man. Tliis is inter- 
esting when we consider the composition of the blood 
and its coagulation in the Aves. The cell upon which 
human coagulation seems to depend, the platelet, is rep- 
resented in birds by the thrombocyte, which appears only 
up to about 50,000 per cubic millimetre. Coagulation time 
is relatively short and the resulting clot is firm and 
irregular. Perhaps this may have something to do with 
the nature of an inflammatory exudate. 
The response to infection on the part of birds may to 
some extent depend upon differences in anatomy, which 
are quite distinct, not only from the mammals within 
which class the anatomy is more uniform, but also from 
one avian order to another. These differences among the 
birds may be exemplified by the large foramina between 
lungs and air sacs in the water birds, a passage which 
permits infection, notably mycosis, to spread from 
the first to the second. Again the close apposition of 
the pancreas to the duodenum over a long stretch 
permits easy infection of the former from the latter. 
Still again the large renal-portal vein in the gallinaceous 
birds explains some of the infections of the liver sec- 
ondary to intestinal disease. The position of the lungs, 
deep in the thorax and fitted into recesses made by the 
sharp anterior border of the ribs and overlaid anteriorly 
