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The results thus obtained admitted no doubt whatever as to tlie responsibility of the
nematodes for the development of growths, nor to the faet that transmission of the nematode
into the rat must take place by the P. americana. Further conclusions as to the part played
by the cockroach during the transmission could not be drawn from these experiments. It
might be possible that the cockroach transmitted the nematode into the rat, without serving
as a host, in which the nematode went through a further development. Numerous examina-
tions of rats, the stomach of which contained nematodes, now showed that eggs containing
embryos were embedded in the squamous-celled epithelium of the cardiac portion of the
stomach. The eggs are hberated by desquamation of the epithelium and pass with the excre-
ments of the infected rats without further development. The excrements nearly always contain
eggs, but never free embryos. It further appeared from the experiments that the eggs, when
left in the laboratory for half a year in moist excrements of the rat did not change at all,
neither did the excrements then contain free embryos.
As already mentioned the first experiments in which the rats were fed on tumour material
from two of the Dorpat rats had given negative results. In later experiments eggs with em-
bryos were used for feeding, but no transmission of the nematode into normal rats was reached.
On the whole investigations had now shown 1) that in excrements evacuated from in-
fected rats no free embryos were found but only eggs containing embryos, 2) that the eggs
directly transmitted into the stomach of rats did not develop into nematodes, 3) that the
eggs when left in the excrements did not go through any further development — • at any rate
not during half a year. The nematode, however, actually being transmitted by the cockroach,
these observations had left it beyond all discussion that the cockroach really served as a
host in the proper sense of the word, and the parasite thus was sure to be found in their body.
Examination of the fatty bodies of the P. americana from the sugar refinery, however,
gave negative results, as well as examination of the digestive tube, which in numerous cases
contained neither eggs nor free embryos. On examination of protorax and the limbs, however,
nematodes, which after their size and shape most likely must be considered further stages of the
embryos, were found in the muscles, coiled up like trichines. As a matter of faet it might be quite
another nematode as well. In order to disprove this, a series of experiments was made to
transmit the nematode into cockroaches, in the muscles of which the absence of nematodes
before the transmission could be absolutely taken for granted. In these experiments P. orientalis
were used, fed partly on eggs extracted from nematodes, partly with rats’ excrements
containing eggs. The cockroaches were examined 42 — 60 days after discontinuance of the feeding.
The experiments are seen from the folio wing table:
Number of
cockroaches
examined
Nematodes
found in the
muscles of
Cockroaches fed on fæces ....
— — eggs
Non-fed control cockroaches. .
18
9
101
17
9
O
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