292 Transactions of the Society. 
though hardly appreciable to Ue naked eye, is easily recognizable 
under a comparatively low amplification. The persistence of the 
vascular wall in the nematode tubercle causes it to retain a sharply 
defined outline, which is quite wanting in that of cestode origin. 
Under a higher power, however, the histological resemblance between 
the substance of the two forms of helminth tubercle to eich other, and 
to true tubercle, are still sufficiently striking. Nor is this at all 
surprising when it is remembered that all three are merely reversions 
of the more specialized forms of connective tissue to embryonic cha- 
racteristics under the stimulus of the presence of parasitic organisms, 
widely different though the latter may be. 
With suitable staining methods, there can, of course, he no 
possibility of confusing the three forms. It is almost needless to 
remark that no schizomycete organisms such as characterize true 
tubercle, are to be met with in the helminth tubercles ; while, on the 
other hand, a sufficiently complete series of sections of the latter will 
never fail to exhibit, somewhere in the series, a characteristic embryo, 
cestode or nematode, as the case may be. 
In cestode tubercle of the liver, where the embryo has but recently 
been deposited in that organ, the vascular origin of tissues forming 
the tubercle is generally quite obvious. Often the vessel can be 
traced up to the embryo, and its walls may be seen, spread out, and 
stretched over the intruder. 
This is tolerably well shown in the last of the series of five 
microphotographs which illustrate this note. The embryo is placed 
almost exactly in the centre of the field, and the portal venule in 
which it is lodged may be traced up to it tolerably clearly, although 
it is placed not in the venule which forms so prominent a feature of 
the section, but in a smaller branch lying close beside it. As may 
be judged from the small amount of tissue proliferation around it, the 
embryo, in this instance, has hardly reached the stage in which it 
would form a nodule visible to the naked eye ; a later condition is 
illustrated in the section of lung (fig. 3) where the gradual fading off 
of the infiltration surrounding the embryo is well shown. Contrary 
to what might be expected, the embryos forming the nuclei of these 
obvious tubercles are, as a rule, in no way notably larger than that 
illustrated in fig. 4. While, too, the latter embryo has obviously been 
killed only by the alcohol used to harden the specimen, the embryos 
contained in the distinct tubercles are, so far as I can ascertain, 
always breaking down, and have clearly been dead for some time 
before the death of the host. It is noteworthy too, in this connection, 
that I have never met with any transition stages between the helminth 
tubercle and the true cystic tumour. The fact is, I take it, that, 
while living, cestode embryos of the size of those under discussion do 
not set up sufficient reaction in the tissues around them to form a 
sufficiently large patch of altered tissue to be visible to the naked 
eye. When they die, however, they act as foreign substances, and 
