Abstract
It is often maintained that after intramammary application of penicillin the excretion of penicillin via the untreated glands takes place by direct diffusion from treated to untreated glands (vide Hawkins et al. 1962, Jacobs & Pennings 1969, Rollins et al. 1970). Blobel (1960) mentions the possibilities of both direct diffusion from gland to gland and the excretion via the blood.