DISEASES OF THE LYMPHATIC TISSUES 125 
mammals proportionately more than in birds, 27 or 1.5 
per cent, to 35 to 1 per cent. 
Reason for Congestive Enlargements. 
Perhaps this is partly due to the circulatory anatomy 
since in the former the arterial and venous supply is 
usually by one large vessel of each kind, whereas in birds 
the splenic branch of the coeliac axis breaks up into several 
small arteries and the venous return is accomplished by 
numerous venules some of which reenter the posterior 
cava almost directly, others joining with the mesenteric 
to form the portal; by this arrangement a more elastic 
system is assured. The same condition is found when 
analyzing the records of chronic passive congestion; in 
eighteen recorded cases, fourteen were mammals and four 
birds. In these cases the principal associated pathologi- 
cal lesions were pleural and pulmonary in seven, cardiac 
in three, renal in three and hepatic in four. While the 
anatomy of the splenic blood supply may help to 
explain the small number of congestions in Aves, it will 
not answer for the inflammations which occur in large 
numbers in this class; this will be discussed in the 
following pages. 
Hemorrhage and infarction of the spleen are not 
very common, there being eleven of the former and ten of 
the latter and all occurring with the same indication or 
history of infectious disease; in one case, an opossum 
{Didelphys virginiana) an injury probably caused a mas- 
sive hemorrhage shaped like an infarct. It is, however, 
curious that of the twenty-one cases only five occurred in 
birds, of which only one hemorrhage was in the shape to 
which the term infarction is best applied. There have 
been, as one might expect, a few cases of infected infarc- 
tion, with abscess. It is perhaps worth noting that no 
case of hemorrhagic cyst or inspissated coagulum has 
been seen. Only one case of rupture is recorded second- 
ary to acute splenitis during an acute septicemia. 
