202 
PULMONARY MODELS 
FiGXJRE 1. — Incident light dark-field microscope with xenon light source and photographic attachments. Note posi- 
tion of thoracic window support. 
into the inner surface of the bobbin (Fig. 2). 
A stainless steel supporting device was then 
constructed which screwed into the bobbin and 
was in turn anchored to vertical support bars 
mounted on our microscope (Fig. 3). The win- 
dow was thus held motionless, and its plane 
perpendicular to the axis of observation. The 
steel support is adaptable to any size window 
since its central portion is removable and can 
be replaced by one of an appropriate size (Fig. 
4). A secondary benefit was achieved by the 
addition of the screw thread. One of the recur- 
ring problems with chronic thoracic windows is 
membrane damage caused by the animal or 
its environment. A rigid Incite cover was made 
that could be securely screwed into the threaded 
bobbin and this prevented that damage (Fig. 
2). 
The final problem, lung motion in the axis 
of observation, was overcome by utilizing a 
highly polished Y^o inch rigid lucite plate as 
the window element instead of flexible 0.5 mil 
teflon. This material is far easier to handle, 
more durable and allows motion only in a 
lateral plane. We continue, however, to protect 
this lucite membrane from the animal's daily 
activities with the thick outer cover. 
RESULTS 
This new window has been successfully left 
in place for three weeks (Fig. 5). Tissue reac- 
tion has been minimal. Optically, light trans- 
mission is on a par with FEP teflon. There is 
minimal back-scatter and no appreciable visual 
distortion. Color rendition is uniformly excel- 
lent. We can now view the lung during active 
respiration in chronic animals breathing on 
their own (Fig. 6) . 
