Adult domestic ducks (Cairina mosch

Adult domestic ducks (Cairina moschata) were purchased
from farmers and transported to the Department of Veterinary
Anatomy and Physiology of the University of Nairobi.
The animals were subjected to the selected investigative
procedures as detailed below (outlined in Table 1). In all
cases, anesthesia was achieved by intra-abdominal injection
of Euthatal (sodium pentobarbitone, injected i.p. at a dosage of 50 mg kg−1 bodymass). All protocols were approved by the
Animal Care and Use Committee of the University.
2.1. Tissue Fixation. Lungs intended for microscopy were
fixed in situ by intratracheal infusion with a solution of
2.5% glutaraldehyde in 0.1M cacodylate buffer (pH 7.4,
350 mOsm) and subsequent immersion into the same
fixative.
2.2. Macroscopic Observations. Lungs were carefully dissected
out by cutting off the ribs. After a general observation,
a longitudinal cutwas made on the ventral aspect of the lung
along the long axis of the intrapulmonary primary bronchus,
thus revealing the internal aspect of the mesobronchus.
Identification and enumeration of the various categories of
secondary bronchi emerging fromthe primary bronchus was
conducted. In addition, lungs were subjected to macrophotography
using a digital camera.
2.3. Light and Transmission Electron Microscopy. Fixed
lungs were sliced into slabs and then diced into small
blocks. Tissue blocks were postfixed in osmium tetroxide;
block-stained with uranyl acetate, dehydrated through
ascending concentrations of ethanol, and embedded in
epoxy resin. Semithin sections were obtained at a nominal
thickness of 1