THE AIR SPACES IN THE LUNG OF THE CAT 
WILLIAM SNOW MILLER 
Anatomical Laboratory, University of Wisconsin 
FOUR PLATES 
Since the time of Hippocrates the lung has been a subject of 
study and discussion. But little was known of its finer struc- 
ture until the discovery of the circulation by Harvey and the 
introduction of the microscope into histological research made it 
possible for Malpighi to publish his letters to Borelli. Then, 
step by step, our knowledge of the finer structure of the lung 
increased: Rossignol, Kélliker, Waters, Schulze, Aeby and others 
contributing to the advancement. 
Rossignol showed in 1847, that the essential part of the 
respiratory tract, that concerned in haematosis, is identical in 
all vertebrates; consisting in each instance of cells or alveoli. In 
the lower vertebrates the structure is simple, the lung consisting 
of a plain sac. According to Renaut the lung of Proteus repre- 
sents an elongated uni-alveolar lung, showing the ideal morpho- 
logical structure of this organ. As we ascend the scale of ver- 
tebrates the lung becomes more complex. In Siren we find what 
Renaut calls the lobular lung in which we have a number of al- 
veoli instead of a single one. In Rana and Lacerta we have the 
single lobar lung. Continuing the ascent of the scale we find 
the organ becoming more and more complex until, in mammals, 
it reaches its highest development. Renaut describes the lungs 
of birds and mammals as being composed of many thousands of 
elementary lungs, such as that of Proteus, that is saccules having 
a respiratory surface. 
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JOURNAL OF MORPHOLOGY, VOL. 24, No. 4 
DECEMBER, 1913 
