Apocrine secretion in the terminal bronchiole of mouse lung.

The question of the existence of apocrine secretory activity by the Clara cells of the mouse lung terminal bronchiole has been investigated in depth. The overall superiority of 1--2 micrometer plastic sections for light microscopy was demonstrated. The preservation of the anatomy of the terminal bronchiole was shown to be adversely affected by slow killing methods, by post mortem delays before fixation, and by the instillation of fluids via the trachea. The use of collapsed lungs removed from rapidly killed animals is probably the best method for the study of the small bronchioles of the lung. Apocrine secretion takes place as originally described by Clara in 1937. The reason why the phenomenon has received so little attention in the literature is probably because the tracheal or vascular perfusion of fixative, and delays before fixation, all prevent apocrine droplets from being preserved.