DISEASES OF THE LYMPHATIC TISSUES 127 
ently make greater use of the organ in defence, and the 
preponderance of acute diffuse hyperplasias in mammals. 
It is noteworthy that the Primates and MarsupiaUa show 
more of the acute hypertrophy of the spleen going under 
the name of tumor. It would be interesting and valuable 
to be able to discover exactly what determines and con- 
stitutes the conditions usually termed hyperplasia and 
inflammation of the spleen and an attempt was made in 
this direction by tabulating the data from Table 7 in 
terms of each diagnosis, classifying these latter also as 
infectious and toxic. The results of this effort are not 
conclusive, and while they permit of some discussion of 
the lesions, do not allow finished conclusions. The figures 
obtained by study are not illuminating. One can state, 
however, that in infections, either specific or not specific, 
more elements of the spleen were engaged in the process 
than when the condition did not resemble a communicable 
disease, but might be called toxic. Under the former 
condition the diagnosis of splenitis or acute tumor pre- 
dominated, while under the latter follicular hyperplasia 
is more often recorded. Anatomical alterations in these 
two groups are described in the definition given in a 
previous paragraph and deserve no special discussion 
except in so far as they concern the changes in the avian 
splenic tumor when under magnification. 
Microscopically there is a total loss of the relations in 
the acute splenic tumor of birds, the chords and follicles 
being replaced by a rather regularly arranged mass of 
small and large mononuclears, granular cells of the circu- 
lating types and red blood cells ; pigment always seems 
increased. Endothelial cells do not take part in the 
general mass of the organ but along lymph and blood 
vessels their bulk and number are increased so that if the 
packing be not too dense one may find double lines of these 
cells passing through the hyperplastic tissue. There is, 
however, a group of seven cases (six birds) to which the 
term endothelial hyperplasia in the spleen has been 
