The small type piroplasma which is known to be prevailing in Korean cattle was injected to un-susceptible hosts such as mice, guinea pigs, rats, rabbits, fowls and developing chicken eggs by i.v. , i.p. and intra C,A. M. routes, and its morphological development in each animal species was observed,
1. The small type piroplasma of cattle did not produce any pathogenicity in the experimental animals such as mice, guinea pigs, rats, rabbits, fowls and developing chiton embryos, However, only a partial sign for developing cycle of the organism was observed in the peritoneal fluid. The schizogony of protozoa was not detected in any organs of the inoculated animals,
2. In the animals inoculated, the parasites of Ⅰ-Ⅲ types, relative to the process of time in the host, have changed their shapes into Ⅳ-Ⅵ types and then Ⅵ-Ⅹ types however, the type Ⅹ was not restored to the type I. In guinea pigs, more grape type was detected then Ⅹ type in number, and in process of time, the shape was changed from round to elliptic, and the pointed end of the organism appeared in flesh color.
3. None of the organisms were found from the blood stream of inoculated animals excepts only a few piroplasma as were found in the experimental mice shortly after inoculation or i. v. route, No protozoa was also found in the organs of the animals autopsied.
4. The form change of protozoa was more clear in these animals than that in susceptible host. The most piroplasmas have changed their forms into Ⅵ-Ⅹ types 30 hours after inoculation and were dispersed from R. B. C. Tracing of piroplasrma beyond this stage was not attempted .
5. The small type piroplasma comprises in Ⅰ. Ⅹ types and it is further believed that ⅩⅠⅩ types which were freed from one cell proceeded to invade others. The from of development resembles to the small type of piroplasma which is prevailing in Japan.
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