J. R. GILLESPIE AND W. S. TYLER 
225 
COLO : "X" 
25 yrs 800 lbs 
0 20 40 60 80 100 0 20 40 60 80 
EXPIRATORY FLOW 
L/sec 
Figure 1. — Thoracic gas volume — flow curves of a 
normal horse (left) and horse with chronic obstructive 
lung disease (COLD) (right). Broken lines are pas- 
sive expirations from total lung capacity. 
ture will be important to our complete under- 
standing of the mechanisms underlying the loss 
of lung function. 
Nowell and co-workers have developed new 
ways of examining the lung with the scanning 
electron microscope (SEM).^'' Figure 2 is a 
SEM micrograph of a section of normal horse 
lung. The principal advantages of the SEM are 
its great depth of focus and wide range of 
magnification which, in the lung, permit large 
numbers of alveoli to be seen in focus at one 
time. It is especially useful for studies of emphy- 
sema, due to the focal nature of the lesions and 
Figure 2. — SEM of normal horse lung. Normal sized 
alveoli and alveolar ducts. 
Figure 3. — SEM of emphysematous horse lung. The 
alveolar walls are fenestrated and sparce. Most inter- 
alveolar septa have been completely destroyed, while 
trabecular strands of tissue are the sole remnants of 
others (1 - O'clock). 
the variation in the amount of destruction of 
adjacent areas. 
Figures 3 and 4 show emphysematous horse 
lung. Fenestrae in the walls of alveoli, alveolar 
ducts, and respiratory bronchioles are recog- 
nized as the earliest and most characteristic 
manifestation of emphysema in man.^^ Isolated 
pieces of tissue apparently floating in alveolar 
spaces are a pathognomonic lesion of emphysema 
in histological sections.^^ This appearance is 
the result of seeing trabeculae in a single plane. 
Figure 4. — SEM of emphysematous horse lung. Rem- 
nants of a destroyed respiratory bronchiole. Only 
vague skeleton of normal lung parenchyma remain. 
