1. The placental blood film examination is worthy of routine application wherever æstivo-autumnal malaria is endemic. This type of malaria when associated with labor and the early days of the puerperium can be more easily and certainly diagnosed by the use of this film and a polychrome stain than by employing the usual films made from the mother's peripheral blood at the time of labor. The placental film in such an infection offers an abundance of adult parasites and far more evidence of the presence of pigment, while the peripheral blood film frequently offers but a scant number of the small ring or discoid forms of a parasite. The examination of the present series revealed positive placental films in nineteen cases, while but eight of these same cases were positive in the peripheral blood film examination. On the other hand, no peripheral blood films were found positive in which the associated placental films did not reveal a far more abundant evidence of the infection. 2. The early days of the puerperium can by this method be protected many times from a malarial outburst, and, as a rule, puerperal sepsis can be differentiated. 3. The intricate vascular architecture of the mature placenta rivals that of the spleen, liver, and bone marrow as a harbor for adult malarial parasites of this type and as a storage for pigment. 4. The localization of parasites in the placenta is unique. Here is the one vascular system which particularly favors the development of the parasites but which at the same time is so situated that it may be spontaneously discarded by the body at the climax of the attack. By this simple act late in pregnancy the prognosis for both mother and child may be improved. 5. The pregnant state encourages attacks of malaria by lowering bodily resistance and by furnishing an additional harbor for the development of parasites. A tenable theory in regard to most attacks of this nature, occurring in cases under professional care, would appear to be the development of latent malaria (malarial carriers) into acute attacks toward the close of the pregnant state. The women who expose themselves (as the negroes in this series) offer favorable conditions to the introduction of a primary infection. Malaria frequently interrupts the late stages of pregnancy and sometimes causes the death of the mother and the fetus, more often the latter. The records at Ancon indicate that it more frequently exerts a harmful influence than other types of infectious diseases in this locality. 6. Most of the children in this series that were delivered while malaria was present in the mother, were of a race that seems to possess a relative immunity to the ravages of malaria. This may account for the fact that the negro fetus more nearly approximates the full term of development when associated with this disease and is comparatively subjected to a less number of the accidents of pregnancy. Many of them revealed evidence of prematurity and were jaundiced, but, as a rule, they developed rapidly. The commonest mishap is miscarriage late in pregnancy. Occasional still-births occur and sometimes there is a fatal issue to both the mother and child. 7. Cases diagnosed as congenital malaria probably indicate that some accident occurred to the placenta, because it practically never happens that fetal blood is positive at the time of birth, regardless of the degree of infection in the mother. Many of the cases now reported in the literature as congenital malaria suggest immediate postnatal infection as their history, as our pathological and clinical records testify. 8. The size of the intervillous spaces of the placenta and their adaptability in the localization of parasites seem to disprove to a certain extent the old idea that the localization depends on the smallness of the capillary caliber. If this were the case the brain should be more often the seat of an extensive localization than the spleen, bone marrow, and placenta, yet our anatomical records will not support that theory. A sluggish blood sinus with a large endothelial surface, a higher internal body temperature, and red blood cells burdened with parasites of a certain age beyond the ring form seem to be important factors in the localization and development of the æstivo-autumnal parasite. 9. The racial disparity of malarial infections shown in this series is believed to be due to local conditions and a wrong impression is apt to be given by our statistics in regard to the relative immunity of the negro race. The white women on the Canal Zone avail themselves of all the opportunities the sanitary system affords; they live well and place the entire course of their pregnant state under competent professional care, while the negro woman is indifferent to her pregnant state, works as a domestic servant, and lives in the cheapest unprotected quarters that can be rented in the suburban divisions of Panama City where the malarial rate is highest and the sanitary control is difficult. It should be noted that these negro women can carry an infection with little manifestation of its presence that would produce serious results in the white women brought from the temperate zone regions of Europe and the United States.