492 DISEASE IN WILD MAMMALS AND BIRDS 
since in the mammal 91.4 per cent, show pulmonary lesions 
while only 53.7 per cent, of birds are so affected. Part of 
the reason for this appears in the figures for the principal 
abdominal organs, of which the liver and spleen occupy 
the prominent places. The mammalian livers show 58.2 
per cent., the avian 80.3 per cent. ; 67.5 per cent, of mam- 
malian spleens, 68.0 per cent, of a\^an spleens have tuber- 
culous lesions. The figure for the mammalian spleen is 
distorted because of the peculiar susceptibility of this 
organ in the monkey, it being conspicuously free of 
lesions in most mammalian orders. The intestines pre- 
sented discernible lesions in practically 40 per cent, of 
birds but only in 13.5 per cent, of mammals. Renal 
involvement was found in 38.4 per cent, of mammals and 
22.9 per cent, of birds. 
A study of the changes in the serous surfaces is com- 
plicated by the difference of anatomy in the two classes. 
The mammal has separate closed serous sacs well guarded 
against invasion from mucous surfaces whereas in the 
bird the air sacs and serous cavities are closely related, 
the latter being loosely applied to viscera they are 
intended to cover. Moreover in Aves direct infection of 
the air sacs seems a definite possibility. Notwithstanding 
the fact that the bird's sacs and serous surfaces appear 
so open to infection there is no great preponderance of 
lesions ^\'ithin them — Aves 39.3 per cent. Mammalia 32 
per cent. The lymph nodes were tabulated as a tissue 
rather than according to location, the latter method be- 
ing found profitable for discussion in a few orders only. 
As might be expected the abundant lymph nodes of the 
mammal were affected out of all proportion to those in 
the bird. These matters will be discussed later. The 
remaining figures on the table have no comparative value. 
Ordinate Characteristics. 
The Primates as an order have shown low resistance 
to tuberculosis, a fact well known to general observation. 
How much this is due to the unsanitary surroundings to 
