638 DISEASE IN WILD MAMMALS AND BIRDS 
ventricle rather than the gizzard of birds corresponding, 
parasitologically speaking, to the stomach of mammals. 
We have found but one parasitic species in the gizzard 
of birds, i.e., immature forms of Spiroptera incerta lying 
under the chitinous lining of the gizzard and only dis- 
coverable after the lining has been peeled off. The peri- 
toneum comes third (air sacs of birds) due to the presence 
of filaridae, and the blood fourth for the same reason. It 
is to be emphasized that, in our data, identical organs 
of mammals and birds should be about equally liable to 
infestment vnth the possible exception of the lungs. But 
in view of the small number of cases available there is no 
justification for speculating about the reason for this 
last difference, albeit the radical difference in the anatomy 
of the two classes is very inviting. 
Now that our spiroptera enzootic has subsided, the 
order above given will be changed, and in view of like 
disturbing factors other gardens should not expect the 
same order to hold invariably for their collection, since 
their enzootics will depend somewhat on the preponder- 
ance of animals of one or another family which are likely 
to compose their exhibits. A single such enzootic may 
suflSce to disarrange the whole fabric, and if two or three 
are taken into account the order of organ involvement 
can be quite disrupted. To attempt to construct statisti- 
cally an '' order of frequency involved " which would 
stand for every garden would only lead to interminable 
adjustments on the basis of animals exhibited and of 
parasitic enzootics, so that I have finally been reduced to 
a combination of our Garden statistics and the blood- 
parasitic ones of the London Garden. Doing this I have 
arranged in Table 27 the frequency of organ involvement 
as follows and estimated the percentage of animals in- 
fested. These figures are computed upon a different basis 
from that of Table 24. They naturally cover all animals 
and not the ' ' susceptible ' ' ones as in Table 24. 
