282 HERBERT G. WILLSON 
form and to have a diameter of 0.2 mm. Since the volume of 
such a sphere is 0.004+ emm., Aeby concludes that in a cubie 
millimeter of lung tissue there would be 250 such alveoli, each 
with an area of 0.125+ sq. mm., so that in a cubic millimeter 
of lung tissue the total area would be 250 x .125 or 31.25 sq. mm. 
Nicolas gives estimates of the different areas of respiratory 
epithelium corresponding to the various degrees of expansion. 
He considers the maximum volume of air which the lungs will 
hold to be 4970 cem. in the average man. Huis statements are 
based on calculations by Aeby: 
Le nombre total des alvéoles est immense. Huschke l’avait évalué 
4 1700 ou 1800 millions. Selon Aeby ce chiffre est beaucoup trop élevé. 
D’aprés ses calculs chaque millimétre cube de poumon comprendrait 
250 alvéoles représentant une surface de 31.2 muillimétres carrés. En 
estimant le volume du poumon a4 1617 centimétres cubes chez l’homme 
et a 1290 chez la femme, on obtiendrait chez le premier une somme totale 
de 404 millions d’alvéoles et chez la seconde de 322 millions, (en chiffres 
ronds). Cette quantité correspondrait 4 une surface de 50 4 40 métres 
earrés pendant l’expiration forcée, de 79 (homme) 4 63 métres carrés 
(femme) pendant l’état moyen de repos, et enfin de 129 (homme) 4 103 
métres carrés (femme) lors d’une dilation compléte. 
The result here given of 129 square meters is greatly in excess 
of my maximum result, in spite of the fact that in the caleula- 
tions of Aeby and Nicolas the figure representing the volume 
of the lungs is smaller. The difference arises from the difference 
in the estimate of the number of square millimeters of area per 
cubic millimeter of lung tissue. Nicolas uses Aeby’s estimate of 
31.2 sq. mm., while my estimate is 14 sq. mm. To obtain a 
result of 31.2 sq. mm., according to my method of calculation, 
the air-spaces cut in an area of 1 sq.mm. would have to be much 
more numerous than those of any of my sections of adult lung. 
F. E. Schulze also refers to Aeby’s calculations. After ex- 
plaining that Aeby assumes the average diameter of an alveolus 
to be 200 u, he states that he cannot agree with Aeby’s estimate 
of the number of alveoli and corresponding total respiratory 
surface. Schulze used his own estimate of the volume, 1500 
cem., for the lungs of the average man. To get the volume of the 
respiratory parenchyma he deducts 20 per cent, leaving 1200 
