6 Mindeskrift for J. Steenstrup. XXV. 



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 



