An Examination of the Proteinase Con- Tent of Human Lymphocytes, Monocytes and Polymorphonuclear Leucocytes

concentration was three times greater than that in the adult at 0.5 h and the difference between the two ages became greater as time passed, rising to tenfold at 8 h. The mean lung concentrations in adult and neonate were similar at 0.5, 1 and 2 h but at 4 and 8 h neonatal lung gentamicin levels were greater than those in the adult. Gentamicin was detectable in adult brain at 0.5 and 1 h only, values thereafter being insignificantly different from zero. In contrast the mean brain gentamicin concentration of the neonates rose progressively to a peak of 1.26 ng/mg at 4 h and had not fallen significantly a t 8 h. In all tissues the extracellular space was significantly greater in the neonate but the degree of difference varied markedly, being greatest in the liver and least in the lung. The renal concentration of gentamicin in both adult and neonate was always in excess of the plasma concentration. In the adult there was no evidence of intracellular gentamicin in heart or muscle, but the mean lung concentration exceeded that in the lung extracellular space by 0.9-3.0 ng/mg at all times studied and the mean ‘intracellular’ gentamicin concentration in liver was 0.5, 1.5 and 1.4 ng/mg at 2, 4 and 8 h respectively. In neonatal lung and muscle ‘intracellular’ gentamicin was detectable from 2 h on and the concentration remained stable at 1.21-2.32 ng/mg. In liver ‘intracellular’ gentamicin was first detected at 4 h when the mean concentration was 1.6 ng/mg, but at 8 h this had risen to 3.71 ng/mg. Cardiac ‘intracellular’ gentamicin was present at 8 h in a low but significant concentration of 0.59 ng/mg.