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Summary. This paper reports a statistical study of mortality and the number of newborns per litter. Two types of mortality were observed in premature mice, mortality at reanimation and breeding mortality. Mortality at reanimation was about 13 % ; breeding mortality, occurring only during the first 3 neonatal days, was of two types : primary neonatal mortality (10.9 %), occurring from the end of reanimation up to 6 h after birth, and secondary neonatal mortality (6.9 %) which appeared from days 2 to 3. The role of some factors causing mortality has been discussed.Introduction.

Summary. This paper reports a statistical and transversal study of After an early, transitory loss of body and organ weights, which occurred during the first neonatal day, the weight handicaps of premature mice were overcome before neonatal day 20 as follows : adrenal weight between 6 h and day 2, liver weight between days 2 and 6, kidney and body weights between days 6 and 20. Throughout these stages, the weight gain of body and organs was higher than that of full-term newborns. The weight gains of premature mice, like those of full-term newborns, were in inverse ratio to the number of newborns per litter. The role of some factors involved in the growth of organs of premature mice has been discussed and the somatic development of surviving premature mice has been compared to that of smallest premature human infants.Introduction.

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