Published online by Cambridge University Press: 06 April 2009
1. Trypanosoma lewisi was found in 25% of rats caught in and about Cambridge. Of these rats 12% were young, 33% adult, and 29% old. In this region the endetnicity was localised to certain areas.
2. Fleas (C. fasciatus and C. agyrtes) were constantly found associated with wild rats infected with T. lewisi. We think that these two species of fleas are the chief carriers of the parasite from rat to rat in this region.
3. We tried transmission experiments with fleas (C. fasciatus and C. agyrtes), lice (H. spinulosus), bugs (A. lectularia), ticks (O. moubata, nymphs and adults), and Gamasus sp., but only obtained a positive result by the agency of fleas.
4. In the transmission experiments the arthropod was transferred from an infected to an uninfected animal. 16% of 138 experiments with fleas were successful, 80—98% of the fleas used were non-infective, while 2—20% were infective.
5. Distant transmission occurs with fleas. This was observed by one of us in January, 1909.
6. ‘Mechanical’ transmission occurs sometimes with fleas.
7. Infective fleas do not transmit the power of infection to their young.
8. The mechanism of infection in the case of mechanical transmission is by the bite of the flea; in the case of the distant infection it is not so.
9. The infective forms of T. lewisi for distant transmission are probably the ‘small trypanosomes’ which we have described elsewhere (1910). The forms of T. lewisi found prior to the small trypanosomes in the developmental cycle are not infective.
10. The development of the trypanosomes in the flea is not interfered with by the flea feeding on a rat immune to the disease.
11. Seventeen experiments with lice were performed, but no transmission was obtained by their agency. 1139 lice were used. No confirmation of Baldrey's infective cycle in lice could be obtained.
12. We could trace no connection between transmission of infection by lice and the presence in them of ‘developmental forms.’
13. No transmission of T. lewisi by other arthropods was obtained. These negative results had no connection with the presence in the arthropods of ‘developmental forms.’
In conclusion we would like to thank Professor Nuttall for his kindness in inoculating our animals and providing us with the material for our experiments, and for his interest and advice in our work.