22 
F. S. BILLINGS. 
This comes to—comes in a lung which has already breathed, and 
in such places in which the supply of air lias been shut oft. The 
mere interruption of the supply of air is not, however, sufficient 
to make a part of the lungs atelectatic of an animal which has 
already breathed; in this case the obstruction of the respiratory 
canal is only a condition to atelectasis. The latter will first come 
to pass when the air posterior to the point obstructed is removed. 
The removal of the air takes place as follows : 
By the foetus the lungs are in an atelectatic condition, that is, 
, the alveolse and bronceoli are so much collapsed that the parietes 
of the same are in opposition with each other. Authors have, in 
times past, considered that the alveolic tissue was made up only 
of connective tissue and elastic fibres, and that muscle fibres were 
only to be found in the bronchi. Molescliatt and Piso Borne 
have, however, shown that non-striated muscle fibres also enter 
into the construction of the parietes of the alveolae. F. E. Schulze 
has described at length the distribution of the same in the lungs. 
From this anatomical construction of the lungs, it results that the 
latter are not alone elastic, but also contractile. The part these 
muscle-fibres play by the expiration is as yet undecided. Briicke 
says, “ the quiet expiration results through elastic force” 
IJpon the lungs we distinguish the highest state of inspiration 
and the most profound state of expiration. In the first the 
thoracic cavity and lungs acquire their greatest extension, and the 
lungs their most extreme amount of air. The most profound 
state of expiration is exactly the opposite. In this the lungs are 
but poorly filled with air, but they are not completely empty, by 
any means. The lungs of the cadaver are in the most profound 
state of expiration; in this condition they also have the tendency 
(endeavor) to still more contract, but the further contraction is 
hindered by the thoracic parietes. The most profound state of 
expiration is therefore no atelectasis. It makes no difference, 
therefore, in which moment of the in- or expiration the supply of 
air is interrupted by the obstruction .of the air passage, as of a 
bronchus ; in every case a part of the lungs filled with air would 
be shut off from the general air circulation in the lungs. In the 
course of time the air disappears from the excluded part of the 
