PEARL-LIKE CONCRETIONS IN TRIPE. N57 
the frozen tissues. Even in the fresh tripe the mucous layer 
had entirely disappeared but the submucous layer and the 
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muscular and serous coats were little changed. The “ pearl” 
was easily cut into sections and the latter showed all the typical 
structure of a fine pearl, such as may be found in shell-fish 
except, of course, that it was composed of concentric lamin 
of hard elastic tissue instead of limy substances. It was em- 
bedded in the submucous layer. 
Round it the ordinary areolar tissue of the submucosa 
had been converted into a thin, compact, fibrous cyst containing . 
flattened nuclei. This appears to have been the formative sac. 
The submucosa thinned out over the “ pearl” but was every- 
where continuous so that it held the latter in its place, whereas 
in the frozen material the submucosa had been rubbed away, 
leaving the pearls lying loose in little cavities from which they 
were easily dislodged. In the latter case the pearls were very 
easily seen because of their iridescence, but in the fresh tissue 
they were covered and were recognised only as protuberances 
above the general level. 
There was no nucleus at the centre of any of these bodies, 
or at least none that could be recognised, so that it is impossible 
to say what was their origin. It is almost certain, however, 
that they are the result of an infection of the tissues of the 
alimentary canal by a great number of organisms which had 
gained admittance into the blood stream, had been carried 
into the small vessels of the submucosa and had been arrested 
there. Irritation followed, no doubt with the formation of a 
formative sac which then acted precisely like the similar 
structure that is the cause of pearl-formation in the tissues of 
shell-fish. This process of death and degeneration of a larva 
may often be seen in fish some species of which are particularly 
liable to infection by Cestode larvae. In the case of such an 
infection (and doubtless others) the events that occur follow 
two lines: (1) The infecting larvae or eggs find their specific 
