8 Mindeskrift for J. Steenstrup. XXV. 



On being consumed by the cockroaches (either P. americana or P. orientalis) tbe embryos 

 are liberated and wander into the striped muscles of the protorax and the limbs. In these 

 localities they are found after six weeks or more as larvæ coiled up trichina-like in spirals 

 and surrounded by a capsule. 



When at this point of time the rats eat tlie cockroaches the larvæ are freed from their 

 capsules and wander into the squamous-celled epithelium of the fundus of the rat's stomach 

 (sometimes also into the epithehum of the oesophagus, tongue and mouth) where after c. 2 

 months the females begin to evacuate eggs containing embryos. 



As mentioned above, morphological investigations on the nematode were made by Hj. Dit- 

 levsen, who has examined worms from the Dorpat-rats, from rats from the sugar refinery, 

 and from black and white rats from various experiments; and finally has defined them as 

 belonging to the very same, hitherto undetermined species of the genus Spiroptera as will be 

 described in the following pages. 



Thus, examination had shown that a causal relationship must exist between the 

 nematode and the tumour-growths as in all cases the tumours were found coincident with 

 the parasite, and growths of the same type had been developed by transmitting the worm 

 into normal rats. 



Out of all in all 118 rats (61 wild and 57 laboratory rats fed on P. americana) 94 har- 

 boured the spiroptera in their stomach. In 39 cases the nematode was the only abnormality 

 observed; in 53 rats anatomicai changes were found simultaneously. On the whole, these 

 changes, with only a few exceptions, represented the very same type as those which had ini- 

 tiated the investigations and to a macroscopical view they only showed quantitatively mutual 

 differences. 



Out of 34 laboratory rats fed on P. americana 22 harboured the nematode not only in 

 their stomach but also in their gullet; in 16 of these rats the mucous membrane of the 

 gullet presented anatomicai changes although of a less definite character than in the fundus 

 of the stomach. In a few cases (4 — 5) the nematode was found also in the epithehum of the 

 tongue, and in 1 case in the epithehal covering of the mouth. 



In no rat was the gullet found affected without the stomach being affected too. 



The nematode was never observed in the pyloric portion of the stomach, in the rest of 

 the alimentary canal, nor in other organs. The nematode in question thus only lives in the 

 upper portion of the rat's alimentary canal, paved with a squamous-celled epithelium. Only 

 once was a Spiroptera found in a vein of the ventral wall; in all other cases the worm and 

 free eggs were only found in the epithelial covering, where it is placed between stratum cor- 

 neum and granulosum, producing irregular canals among the cells. Most frequently it is quite 

 covered by the epithelium, but sometimes it may be seen protruding into the cavity of the 

 fundus of the stomach. Very seldom it reachea further down touching the lower coats of the 

 epithehum. 



The anatomicai changes of the stomach (figs. 10 — 16) were found only in the fundus, the 

 pyloric portion being always quite normal. 



In order to obtain a general view, the pathological changes in the rats fed on P. ame- 

 ricana may be divided into: 1) slight changes, (16 rats) 2) definite changes (23 rats) 3) violent 

 changes and tumour growths (16 rats). These groups, however, very smoothly pass into each 

 other without sharp lines of demarcation. Out of the 16 rats fed on great quantities of årti- 



