Abstract
The red blood cells of the mammalian fetus are constantly larger than those of adults of the same species, and resemble very closely the erythrocytes found in individuals with pernicious anemia. 1 It has likewise been shown experimentally that the mean maximal diameter of erythrocytes of newly born rats can be reduced at birth by the administration of concentrated normal gastric juice to the mother during pregnancy. 2
The inaccessibility of common mammalian fetuses to direct injection made it desirable to devise a scheme by which anti-anemic principles could be injected directly into the developing animals themselves. The opossum (Didelphis virginiana) is suitable for this purpose because intrauterine life lasts only 10.5 ± 1.7 days, after which the immature young live in the maternal pouch for 90 days. 3
Materials and Methods. Forty-nine immature opossums, varying in crown-rump lengths from 5.5 to 7.0 cm, were used in these experiments. Twenty were injected over periods varying from 3 to 13 days with 0.8 to 2.2 cc of concentrated normal human gastric juice. Ten untreated pouch mates served as controls. Nine were injected over periods varying from 3 to 14 days with from 0.3 to 2.6 cc of concentrated solution of liver extract. Ten untreated litter mates served as controls. In addition, the cardiac blood of 10 untreated adult animals was examined.
Samples of blood were obtained from the tails of the immature animals before and 2 days after each series of injections. In both immature and adult groups of animals the mean maximal diameter of the erythrocytes was determined by direct measurement and the mean corpuscular volume was calculated. The data thus obtained were analyzed statistically. 4
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