TERMINALS OF HUMAN BRONCHIOLE 283 
ecm. He takes the volume of an alveolus to be 200% cubic microns. 
Reducing the 1200 cem. to cubic microns, he divides the volume 
of a single alveolus into this total volume and arrives at the 
conclusion that there are 150 million alveoli in the lung, thus: 
12 << 10% 
- = 150,000,000 
293 x 106 
He then calculates the area of an alveolus as 5 x 200? square 
microns, and estimates the total respiratory surface as 5 xX 
200? & 150,000,000 square microns, or 30 square meters. 
The estimates of Schulze and Zuntz are much higher than mine 
in proportion to the figures which they use for the volume of the 
lung. 
In our calculation it was found that in the adult, a cubie milli- 
meter of lung tissue represented the following area of lining 
of air passages: 
69346 20 
—— = 13.869 sq. mm., or nearly 14 sq.mm. 
100 1000 
Similar calculations were made of the corresponding area in 
the child’s lung, and estimates were made also from sections of 
emphysematous human lung and from the lung of an opossum. 
The results are given below. 
ADULT NORMAL CHILD MAN OF 61, EMPHYSEMATOUS OPOSSUM 
14 sq.mm. (nearly) 19 sqa.mm. 6 sq.mm. to 8.713 sq.mm. 27 sq.mm. 
| 
Some of the tracings on which these calculations are based 
are reproduced in figures 5 to 9. 
In the child’s lung only a few typical sections were counted, 
and only one reading was taken of the opossum lung. 
In the emphysematous lung, the total perimeters of twenty- 
five consecutive sections were counted, the sections being of 
tissue near the pleura, though there were other parts, also near 
the pleura, where the emphysema was much more marked. 
The readings of the twenty-five squares gave a total of 21784 
mm., an average of 871.3 mm., which corresponds in the actual 
