DISEASES OF THE LYMPHATIC TISSUES 115 
search but they do not possess nodal arrangement and 
capsule. Lymph folhcles on the other hand, are 
quite numerous in the respiratory, and especially, the 
intestinal tract. Groups of follicles may also be found 
in the lining of the upper ends of these tracts in such 
situations that the names faucial, pharyngeal, or even 
tubal tonsils are justly applied. I do not find any ref- 
erence to a lingual tonsil in birds, but this structure is 
found, with of course many modifications, down as far as 
the monotremes. The lymphoid tissue of the naso- 
pharyngeal region is so placed in animals as to be 
exposed to aerial and food infections, just as it is in man. 
It is, however, noteworthy that chronic inflammations 
leading to hypertrophy or to obstruction have not come 
to our attention. There is onlj^ one diagnosis of chronic 
tonsilitis in our records, a determination based upon the 
nodular red brown prominence of the tonsillar region, but 
there were no true hypertrophy and areas of fibrosis com- 
bined with necroses as seen in human medicine ; this case 
concerned a Chacma baboon. 
Hypeeplasia. 
In so far as the reaction to infectious or toxic agents 
is concerned there seems to be a fairly uniform character 
through the mammalian groups, but in the Aves there 
are a few differences worthy of mention. It is at once 
admitted that these observations upon birds are based 
upon a very few sections of isolated lymphatic tissue, 
but they are supported by records of the changes in nodes 
in mucous membranes and viscera, and by those in the 
spleen. The first and perhaps most noteworthy difference 
is in the paucity in birds of large mononuclears of the 
endothelial type. Their position in chords, sinuses and 
germinal centres is taken by deeply staining mono- 
nuclears, of the size and general character of large 
lymphocytes as seen in the blood. The hyperplasia in the 
follicles is much more dense but it is outdone by that in 
