| Abstract
| - Abstract. 1. Over 500 cases of pregnancy occurring in native women of hyperendemic malaria areas of Kenya Colony were studied and the placentas examined in order (a) to observe the reaction of the R.E. system, (b) to observe the nature of the immunity and (c) to determine the origin of the placental R.E. cells. 2. The case with which the immunity of different malaria phases can be studied by this method is explained. 3. The well-known picture of schizonts and R.E. phagocytosis is not seen until the 4th month of pregnancy. 4. The characteristic reaction is associated only with P. falciparum infections, which closely resemble those occurring in culture or in malignant forms of the disease. The presence of “ectoplasmic” forms and the absence of crescents are particularly to be noted. 5. The process of immunity is traced from inception to establishment, and it is seen inter alia that there is no R.E. response at the beginning of a new attack (in spite of the presence of numerous schizonts) but that a response occurs immediately at the beginning of a relapse. 6. The largest number of R.E. cells is found in chronic malaria, when there has been a fairly heavy infection in the blood throughout pregnancy. 7. The theoretical possibilities in regard to the origin of the placental phagocytes is considered and an origin from lymphocytes conveyed to the placenta by the blood stream is established. 8. The transformation occurs in situ; and all stages between the large lymphocytes and the mature R.E. cells are seen in the intervillous spaces. 9. The morphology and vital staining reactions of the placental elements are described. 10. The significance of the high lymphocyte counts in tropical bloods is pointed out. 11. Relapses of malaria following parturition are probably due to the expulsion with the placenta of a highly active R.E. system of defence. 12. Experiments with trypan blue demonstrated the lack of affinity of this dye for the placental phagocytes and the consequent invalidity of certain blockade experiments. 13. The R.E. cells stain readily with neutral red, however, even in severe forms of the disease and complete blockage with malarial fragments is never seen. The theory that death in such cases is due to a blocked R.E. is therefore probably incorrect. Hyperplasia is very evident in fatal cases and there seems to be no intrinsic failure in the R.E. mechanism. 14. Certain peculiarities in the effect of trypan blue are described, including the constant staining of the foetus, the remarkable periodicity of excretion of the dye in the urine and its therapeutic action in chronic malaria. 15. Over 400 cases were investigated to see if congenital malaria occurred. No placental transmission of the malarial parasite, Spirochaeta duttoni or microfilaria could be found. In 17 abortions, the spleens and brains of the infants were likewise negative.
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