45 Human mitotic chromosomes from leucocyte cultures were harvested in the routine manner, and the slide preparations were air-dried for 2-4 hours. They were then placed for 10 minutes in a Coplin jar containing a 50 g. per ml. solution of collagenase (type i, Worthington Biochemical Corporation) prepared in Ca++ and Mg++ free Hanks’ solution, pH 6-5. After several rinses in Hanks’ solution, the preparations were stained for 6 minutes in a 2% solution of Giemsa stain prepared in phosphate buffer, pH 6-8. The resulting chromosome bands were similar to the G bands produced by trypsin. This procedure permits the chromosomes to be banded the day they are harvested without pretreatment. The application of this technique in evaluating the chromosomes from amniotic-cell cultures is extremely valuable, because time is critical in prenatal chromosomal diagnoses. on

Center for Disease Control, Public Health Service, U.S. Department of Health, Education, and Welfare, Atlanta, Georgia 30333, U.S.A.

SUZANNE TRUSLER.

NEONATAL HYPERBILIRUBINÆMIA AND

OXYTOCIN

SiR,—It is not to be expected that an association between the use of oxytocin in labour and neonatal jaundice would be demonstrable by the observation of mean bilirubin concentrations as attempted by Dr Gray and Dr Mitchell (Nov. 9, p. 1144). The incidence of hyperbilirubinaemia (bilirubin > 12 mg. per 100 ml.) in our prospective series 1,2 of 1353 babies was only 8-35%, which is of the same order as that reported by other workers.3,