In nearly 50 per cent. of the cases, virulent trypanosome virus inoculated directly through the stomach wall of rats failed to infect these animals.
The percentage of infections after inoculation of this kind seemed to vary with the virus. Surra of India proved to be the most virulent, and caderas the least. Nagana and dourine occupied intermediate positions.
The rats that escaped infection showed no trace of immunity when tested with small quantities of the same virus between the twelfth and the twenty-eighth days after the intra-stomachal inoculations.
The majority of the rats tested for immunity with surra of India and nagana seemed to have acquired, instead of an immunity, a certain hypersensitiveness to infection. Five of the seven nagana rats died before their controls.
The results of testing the vitality of the trypanosomes of caderas, dourine, and nagana introduced directly into the stomachs and intestines of living rats seem to show that both motility and virulence are usually lost in less than two hours. Surra of India proved exceptionally resistant to the harmful influences of the stomach, for in one case, surra trypanosomes introduced into the intestines were found to be sluggishly motile in the stomach one hour and fifty-five minutes later, and in another instance, surra parasites injected into the stomach were found, when removed from that organ two hours later, to be actively motile and infectious.