Variations in diurnal rhythm of leucocytes in white Leghorn chicks of two different ages.

Blood leucocytes in 4-week-old and 5-7-month-old White Leghorn cockerels show a diurnal rhythm. This diurnal rhythm has been observed to vary with age. The variations observed may be due to the different hormonal status of the two groups of birds. The effects of drugs at different phases of the diurnal rhythm will be of great interest in medical practice and should be considered during clinical treatment.