1. Suspensions made from infected caecal material, derived from chickens which had been artificially infected with Histomonas meleagridis by the administration of embryonated Heterakis ova, can be used to transmit the organisms to other chickens when administered per os.
2. Infections with histomonad suspensions can only be obtained in chickens that have been starved, or in chickens that are feeding but have received an alkali mixture immediately before the suspension is administered. The highest incidence of infections is obtained by administering suspensions to starved chickens that have received 1 g. alkali mixture beforehand.
3. Successful infection appears to depend upon the pH of the gizzard and, possibly, of the upper intestine. The incidence of lesions produced by feeding suspension is increased as the contents of the gizzard become alkaline. It is also suggested that the consistency of the food may play a part, as coarse food, along with the infective material, is retained in the gizzard until it is completely ground up and mixed with the gastric juice.
4. In one series of passages the suspension became attenuated after fourteen passages through chickens. In other cases suspensions became attenuated after only six passages through chickens.
5. The courses of infections produced by histomonad suspensions and Heterakis ova are compared.
6. The advantages of the method of using histomonad suspensions are discussed in their relation to the screening of chemotherapeutical agents.
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